Thin Mint Cookie Bars Recipe with Chocolate Ganache

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Why I Love These Chocolate Mint Squares

1. Fudgy & brownie-like: These cookie bars are a hybrid of cookie and brownie — thick, chewy, and dense. They’re based on a fudgy cosmic brownie cookie recipe but pressed into a 9×13 pan to make mint chocolate cookie bars.
2. Balanced mint: Just 1/4 teaspoon peppermint extract in the coating gives a pleasant Thin Mint flavor without overwhelming the chocolate.
3. Great for a crowd: A 9×13 pan can be cut into 12 large squares, 24 medium squares (recommended), or 48 small sticks—perfect for parties or bake sales.

More Girl Scout–inspired recipes: Try Ritz cracker thin mints or a giant thin mint cookie cake for other fun variations.

Ingredient Notes

Overview: This section highlights key ingredient choices. Scroll to the recipe card below for exact measurements and full instructions.

• Cocoa powder: I recommend dark cocoa (Hershey’s Special Dark) for a deeper, fudgier chocolate flavor. Regular unsweetened cocoa will work but produces a puffier, less brownie-like texture.
• Light corn syrup: A small amount helps create the dense, chewy texture. If you prefer not to use corn syrup, thick honey is a workable substitute. Light corn syrup is not the same as high-fructose corn syrup.
• Chocolate chips: Semi-sweet chips are used for the coating; use milk chocolate for a milder finish if you prefer.
• Peppermint extract: Use peppermint extract for a classic Thin Mint flavor. I don’t recommend spearmint for this recipe.

Gluten-free option: Substitute a reliable 1-to-1 gluten-free baking flour to make these bars gluten-free.

Step 1: Make the Dough

In a large bowl, use an electric mixer to cream the butter and sugars, then add eggs, vanilla, and light corn syrup. Mix in baking powder and salt, then fold in dark cocoa powder and all-purpose flour. The dough will be thick and slightly sticky.

1. Preheat oven to 350°F.
2. Cream 3/4 cup softened unsalted butter, 3/4 cup light brown sugar, and 3/4 cup granulated sugar for about 2 minutes until light and fluffy.
3. Add 2 large eggs, 2 teaspoons vanilla, and 3 tablespoons light corn syrup; mix on low until combined.
4. Stir in 1 teaspoon baking powder and 1/2 teaspoon salt.
5. Mix in 3/4 cup dark cocoa powder and 2 1/4 cups all-purpose flour until just combined.

Tip: Using softened butter helps the dough come together more easily; microwave for 10 seconds if needed.

Step 2: Press Into Pan & Bake

Prepare a light-colored metal 9×13 pan with cooking spray and parchment paper, leaving a 2-inch overhang for easy removal. Drop the dough by tablespoonfuls into the pan and press to an even layer. Bake at 350°F for 18–22 minutes, until the center no longer looks wet. Cool completely before adding the coating.

Tip: If the dough is sticky, spray your hands or place a sheet of parchment on top while pressing to smooth the surface.

Step 3: Microwave Coating

Combine 1 cup chocolate chips and 1/4 cup (1/2 stick) unsalted butter in a microwave-safe bowl. Heat at 50% power in 30-second intervals, stirring between each, until smooth. Stir in 1/4 teaspoon peppermint extract. Reserve about 2 tablespoons of the melted chocolate for drizzling.

Tip: Melting at reduced power helps prevent the chocolate from seizing. If the coating seems too thick to spread, stir in 1 tablespoon melted butter to thin slightly.

Step 4: Decorate & Drizzle

Spread the melted chocolate over the cooled bars, covering top and sides. Place the reserved 2 tablespoons of chocolate into a small piping bag or a zipper bag with a tiny corner cut, then drizzle over the top for a finished look.

Step 5: Chill & Cut

Chill the coated bars in the refrigerator or freezer for about 30 minutes to set the chocolate. For clean slices, dip a sharp knife into hot water between cuts and dry it with a paper towel. Press straight down to cut—don’t saw.

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Tips & Variations

• Add mix-ins: Stir up to 3/4 cup chocolate chips, mini chips, or Andes mint chips into the dough for mint chocolate chip bars.
• Decorate: Top with green sprinkles or crushed thin mint cookies for holidays or themed gatherings.
• Serving sizes: Cut into 12, 24, or 48 pieces depending on how large you want each serving.
• Mint-free version: Omit the peppermint extract to enjoy plain fudgy chocolate bars.

Frequently Asked Questions