Preheat the Oven: Preheat the oven to 350°F. Grease an 8x8-inch baking pan or line it with parchment paper.
Make the Brownie Layer: In a medium saucepan, melt 1/2 cup unsalted butter over low heat. Remove from heat and stir in 1 cup semi-sweet chocolate chips until melted and smooth.
Add Sugar and Eggs: Stir in the 1 cup packed light brown sugar, 2 large eggs, and 1 teaspoon pure vanilla extract until well combined.
Incorporate Dry Ingredients: Fold in 1 cup all-purpose flour and 1/2 cup dark cocoa powder until just combined.
Bake the Brownies: Pour the brownie batter into the prepared pan. Bake for 20 minutes, or until a toothpick inserted in the center comes out mostly clean. Let the brownies cool completely in the pan.
Make the Cookie Dough: While the brownies cool, cream together the softened 1/2 cup unsalted butter and 1 cup packed light brown sugar in a large mixing bowl until light and fluffy. Mix in the 1 teaspoon pure vanilla extract.
Finish the Dough: Stir in the 1 cup all-purpose flour and 1 teaspoon kosher salt until just combined. Fold in the 1 cup semi-sweet chocolate chips.
Assemble the Layers: Spread the cookie dough evenly over the cooled brownie layer. Press gently to create a smooth top.
Chill Before Serving: Refrigerate for at least 1 hour to firm up the cookie dough layer before slicing and serving.
Notes
Storage: These brownies store best in the refrigerator due to the cookie dough layer. Keep in an airtight container for up to 5 days.Freezing Instructions: Cool completely, wrap individual bars tightly in plastic wrap, and place in a freezer-safe container or bag. Freeze for up to 3 months.Assembly Tip: Make sure the brownies are completely cool before adding the cookie dough. This keeps the layers clean and prevents the dough from melting.Flour Safety: Because the cookie dough layer is not baked, consider heat-treated flour to make it safe to eat. You can heat-treat flour at home by baking it on a sheet pan at 350°F for 5–7 minutes, then cooling completely before using.Flavor Ideas: Try mixing different chocolate chips into the cookie dough — white chocolate, dark, or milk chocolate all make delicious additions.