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Why These Chocolate Mint Squares Will Become Your New Favorite

These aren’t just any cookie bars; they are the result of careful crafting to deliver maximum flavor and an unforgettable texture. Here’s why these chocolate mint squares stand out from the crowd and why I absolutely adore them:

1. Fudgy & Perfectly Brownie-like: The debate between calling these “cookies” or “brownies” is a delicious one because they truly are a magnificent hybrid. The base is an adapted version of my hugely popular fudgy cosmic brownie cookie recipe, expertly scaled up and thickened to create a substantial, incredibly moist 9×13 pan of mint chocolate cookie bars. Expect a dense, chewy texture that melts in your mouth, far more satisfying than a typical cookie.
2. The Ideal Mint Balance – Not Too Minty: Achieving the perfect peppermint flavor is key, and it’s something I’ve perfected in this recipe. Just a quarter teaspoon of high-quality peppermint extract in the chocolate coating is all it takes. This ensures you get that authentic Thin Mint zing without it becoming overwhelmingly like toothpaste. It’s a delicate balance that allows both the rich chocolate and refreshing mint to shine.
3. Effortless Entertaining – Perfect for a Crowd: If you’re looking for a dessert that’s easy to make and even easier to share, these Thin Mint Cookie Bars are your answer. A single 9×13 pan offers incredible versatility. You can cut them into 12 generous large squares for a substantial treat, or divide them into 24 smaller, perfectly portioned squares (which is my preferred method for these!). For bite-sized delights, you can even cut each of those squares in half to yield 48 delightful cookie sticks, ideal for parties, potlucks, or an impressive dessert spread.

Craving more Girl Scout cookie-inspired delights? You absolutely must try these Ritz cracker thin mints for a quick and easy fix, or make a show-stopping statement with my giant thin mint cookie cake!

Essential Ingredient Notes & Smart Substitutions for Your Thin Mint Bars

Creating these incredible Thin Mint Cookie Bars starts with understanding the role each ingredient plays. This section provides detailed notes and potential substitutions to ensure your baking success. For precise measurements and condensed instructions, please jump down to the full recipe card at the bottom of the post.

• Cocoa Powder: For that signature deep, rich, fudgy flavor and moist texture, I wholeheartedly recommend using Hershey’s Special Dark Cocoa powder. This is a Dutch-processed cocoa, which means it’s less acidic and contributes to a darker color and a smoother, more intense chocolate flavor. While you *can* substitute with regular unsweetened cocoa powder, please note that your cookie bars will likely have a slightly puffier texture and won’t quite achieve that iconic, dense brownie-like taste that the dark cocoa provides.
• Light Corn Syrup: This might seem like an unusual ingredient for cookie bars, but trust me, it’s a secret weapon! We use a small amount of light corn syrup to create that unbelievably chewy, dense, and fudgy texture that sets these bars apart. Omitting it will significantly alter the final texture, so I highly recommend including it. (A quick and important note: light corn syrup is not the same as high fructose corn syrup and is commonly found in the baking aisle – Karo or a generic brand works perfectly). If you absolutely cannot find it or prefer not to use it, a thick honey can achieve a somewhat similar, though not identical, chewy texture.
• Chocolate Chips: My go-to for the coating is semi-sweet chocolate chips, as they provide a balanced chocolate flavor that pairs beautifully with the mint. However, if you prefer a sweeter, more subtle chocolate profile, milk chocolate chips would be a delicious alternative for the topping. For a bolder, less sweet coating, you could even opt for dark chocolate chips.
• Peppermint Extract: The quality of your peppermint extract matters, but don’t fret too much over brands. What’s crucial is to ensure you’re using peppermint extract, not spearmint. Spearmint has a distinctly different flavor that, when combined with chocolate, can unfortunately taste a bit too much like toothpaste, which is definitely not what we’re aiming for in these delicious Thin Mint Cookie Bars!

Make it Gluten-Free! For those with dietary restrictions, these Thin Mint Cookie Bars are easily adaptable. Simply swap out the all-purpose flour for your favorite gluten-free flour blend. My top recommendation is Bob’s Red Mill Gluten Free 1-to-1 Baking Flour. Many bakers have used this particular blend with great success in my cosmic brownie cookie recipe, and it performs beautifully here as well, yielding equally fudgy and delicious results!

Step 1: Prepare the Rich, Fudgy Dough

The foundation of these incredible Thin Mint Cookie Bars is a thick, rich, and slightly sticky chocolate dough. A stand mixer is recommended for ease, but a powerful handheld mixer can also work with a little extra elbow grease. The dough’s unique consistency is what gives these bars their signature fudgy texture.

1. Begin by preheating your oven to 350°F (175°C).
2. In a large mixing bowl, using an electric mixer on medium-high speed, cream together your softened unsalted butter (¾ cup, equivalent to 1 ½ sticks), light brown sugar (¾ cup), and granulated sugar (¾ cup). Beat this mixture for a full 2 minutes until it becomes light, fluffy, and noticeably pale. This creaming process incorporates air, contributing to the bar’s tender crumb.
3. Reduce the mixer speed to low. Add the eggs (2 large), vanilla extract (2 teaspoons), and light corn syrup (3 tablespoons). Mix until just combined. Be sure to scrape down the sides and bottom of the bowl thoroughly with a spatula to ensure all ingredients are fully incorporated and prevent any dry pockets.
4. Next, add the baking powder (1 teaspoon) and salt (½ teaspoon). Mix for another 5-10 seconds until these dry leavening agents are just combined. Note: we’re using baking powder, not baking soda, which affects the texture.
5. Finally, add the star of the show: dark cocoa powder (¾ cup) and all-purpose flour (2 ¼ cups). Mix on medium speed until the flour streaks have just disappeared and a thick, uniform dough forms. Avoid overmixing, as this can lead to tougher bars.

Baking Tip: The consistency of your butter is crucial! Ensure your unsalted butter is genuinely softened – it should yield easily when pressed, but not be melted. If it’s too cold, microwave it in 10-second intervals until slightly softened, but never fully liquid.

Step 2: Press into Pan & Bake to Perfection

Proper pan preparation is essential for easy removal and clean-cut bars. Don’t skip the parchment paper!

First, lightly spray a light-colored metal 9×13 pan with cooking spray. This initial spray helps the parchment paper adhere. Then, line the pan with parchment paper, making sure to leave a generous 2-inch overhang on both long sides. This overhang creates handy “slings” that will allow you to easily lift the entire slab of cooled bars out of the pan, making cutting a breeze.

The dough is thick, so to spread it evenly, drop it into the prepared pan in approximately 1-tablespoon-sized chunks. This makes it easier to distribute. Once all the dough is in the pan, gently press it down and spread it out evenly across the bottom, ensuring a smooth top surface. Bake the bars at 350°F (175°C) for 18-22 minutes. The bars are ready when the edges are set and the center no longer looks visibly wet. Don’t worry if the very center appears a tiny bit underdone; the residual heat from the hot pan will continue to cook the bars as they cool, ensuring a perfectly fudgy interior. Allow the baked bars to cool completely in the pan before attempting to decorate them.

Spreading Tip: This chocolate dough is naturally a bit sticky. To make spreading easier and prevent it from adhering to your hands, I highly recommend either lightly spraying your hands with cooking spray or placing another piece of parchment paper directly on top of the dough and using your hands to gently press down and spread it evenly across the pan.

Step 3: Create the Signature Chocolate Mint Coating

The delicious, refreshing mint coating is what transforms these chocolate bars into the iconic Thin Mint-inspired treat. Achieving the right consistency and flavor balance is key.

In a small to medium-sized microwave-safe bowl, combine your chocolate chips (1 cup) and unsalted butter (¼ cup, or ½ stick). Place the bowl in the microwave and heat on 50% power for 30-second increments. It’s crucial to stir the mixture thoroughly between each interval, even if the chocolate doesn’t appear to be melting during the first few rounds. This slow, controlled melting process at 50% power is vital to prevent the chocolate from seizing (becoming thick and grainy) or burning, ensuring a smooth, glossy coating. Continue until the chocolate and butter are fully melted and completely smooth.

Once your chocolate mixture is perfectly melted and smooth, stir in the ¼ teaspoon of peppermint extract. Mix until it’s evenly distributed. Before you spread the coating over the bars, remember to set aside approximately 2 tablespoons of this melted chocolate. This small amount will be used later for a decorative drizzle, adding an extra touch of elegance to your Thin Mint Cookie Bars.

Coating Consistency Tip: It’s important to note that this chocolate mint coating is designed to be slightly firmer than a typical ganache. This allows it to set up beautifully and create that satisfying “snap” similar to a real Thin Mint. If, after melting and stirring, your mixture appears too thick to spread easily, you can add an additional 1 tablespoon of melted butter, stirring it in until you reach a more workable consistency.

Step 4: Decorate & Drizzle for a Polished Finish

Now comes the fun part – transforming your plain chocolate bars into a visually appealing dessert. A little attention to detail here goes a long way in making these Thin Mint Cookie Bars truly shine.

Carefully spread the prepared melted chocolate mint coating evenly over the completely cooled cookie bars. Use an offset spatula or the back of a spoon to ensure the top and sides are thoroughly covered in a smooth, consistent layer. Take the 2 tablespoons of reserved melted chocolate and transfer it to a small piping bag. If you don’t have a piping bag, a ziploc bag with a tiny corner snipped off will work just as well. Drizzle this reserved chocolate over the top of the coated bars in a decorative pattern – criss-cross lines, zigzags, or swirls – to add an appealing visual flourish and professional touch to your homemade Thin Mint Cookie Bars.

Step 5: Chill, Cut, and Serve Your Fudgy Thin Mint Cookie Bars

Patience is a virtue, especially when it comes to cutting perfectly clean slices of these delectable bars. Allowing the chocolate coating to fully harden is paramount for neat presentation.

To ensure the chocolate coating sets firmly and provides crisp, clean slices, it’s highly recommended to refrigerate or freeze the entire pan of bars for at least 30 minutes. This chilling time solidifies the coating and makes the bars easier to handle. Once adequately chilled and set, remove the pan from the refrigerator or freezer. Using the parchment paper overhang, carefully lift the entire slab of Thin Mint Cookie Bars out of the pan and place it on a cutting board.

Pro Tip for Clean Slices: For impeccably clean and smooth cuts every time, employ this simple chef’s trick: fill a tall cup with very hot water. Before each cut, dip your knife into the hot water, then quickly wipe it completely dry with a paper towel. The warm, dry blade will glide through the chocolate coating and fudgy bar without dragging or smearing. When cutting, avoid a “sawing” motion. Instead, press the knife straight down through the bars with firm, even pressure, then gently lift it straight back up. Repeat this process, wiping and re-warming the knife between each cut, until you’ve sliced all your delicious Thin Mint Cookie Bars into your desired portions.

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Tips, Tricks & Delicious Variations for Your Thin Mint Bars

Once you’ve mastered the basic recipe for these incredible Thin Mint Cookie Bars, there are many ways to customize, enhance, and store them for future enjoyment. Here are some of my favorite tips and variations:

• Elevate with Extra Chocolate or Mint Chips! If you’re a true chocolate chip enthusiast, don’t hesitate to fold in additional chocolate chips, mini chocolate chips, or even Andes mint chips into the dough. This will transform them into decadent mint chocolate chip brownie bars. I’d recommend adding no more than ¾ cup of mix-ins to ensure the dough maintains its perfect texture.
• Seasonal Toppings & Decorations: Jazz up your Thin Mint Cookie Bars for any occasion! For a festive touch, especially around St. Patrick’s Day or Christmas, sprinkle green sprinkles or crushed Thin Mint cookies (or their delicious Keebler copycats) over the wet chocolate mint coating before it sets. This adds both visual appeal and an extra layer of texture.
• Portion Control – Cut Them Your Way! While you certainly can cut these into 12 large, substantial squares, I find that the smaller 24-square size is absolutely perfect for these rich Thin Mint Cookie Bars. For serving at parties or for a bite-sized treat, consider cutting each of those 24 squares in half to create 48 scrumptious, easy-to-handle cookie sticks! This versatility makes them ideal for any gathering.
• A Non-Minty Chocolate Treat: If you find yourself making and loving this fudgy cookie bar base, remember that you can easily make a regular chocolate version! Simply omit the peppermint extract from the chocolate coating for a classic, rich chocolate bar that’s equally delicious. This is a fantastic option if you want to cater to different taste preferences or just enjoy a pure chocolate experience.
• Storage for Freshness: These Thin Mint Cookie Bars store beautifully. Keep them in an airtight container at room temperature for up to 3-4 days. While not strictly necessary, refrigerating them can extend their freshness and enhance their fudgy, chewy texture even further, especially in warmer climates.
• Freezing for Later: Yes, you can freeze these! Once the bars are completely set and cut, arrange them in a single layer on a baking sheet and freeze until solid (about 1-2 hours). Then, transfer the frozen bars to a freezer-safe airtight container or bag, separating layers with parchment paper to prevent sticking. They will keep well in the freezer for up to 2-3 months. Thaw at room temperature or in the refrigerator before serving.
• Gifting Idea: These bars make a wonderful homemade gift! Stack a few squares in a decorative box or tie them with a ribbon for a thoughtful present that any Thin Mint lover will adore.

Frequently Asked Questions About Thin Mint Cookie Bars: