½ cup (1 stick) butter, softened to room temperature
½ cup brown sugar
¼ cup white sugar
1 teaspoon vanilla extract
1¼ cups all-purpose flour
¼ teaspoon salt
½ teaspoon baking soda
1 cup semisweet chocolate chips
16 chocolate crème-filled sandwich cookies (such as Oreo)
1 box brownie mix plus ingredients to prepare mix (see note)
Heat oven to 350 degrees. Line a 9-inch square baking pan with parchment paper and lightly spray with nonstick cooking spray; set aside.
In a medium mixing bowl cream together butter and sugars using an electric mixer until light and fluffy. Add eggs and vanilla and mix to combine.
In a small bowl, mix together the flour, salt and baking soda. Add to butter mixture and mix until all the flour is incorporated. Stir the chocolate chips into the flour/butter mixture; scrape dough into the prepared pan.
Lightly moisten fingertips with water and pat cookie dough into an even layer in the pan. Lightly press sandwich cookies onto top of cookie dough. You should have four rows of four cookies side-by-side. Set aside. In another bowl, prepare brownie mix according to package directions. Pour brownie batter over the cookie layer in pan. Spread evenly and smooth out top. Place pan in oven and bake for 45-50 minutes or until a toothpick or cake tester inserted near center comes out clean. Cool brownies in pan and place on a cooling rack. Cool completely to room temperature.
Using the edges of parchment paper, lift brownies from baking pan. Cut into 16 squares, and then cut squares on the diagonal into triangles.
Cook's note: Use a brownie mix that yields an 8- or 9-inch square pan of brownies. Do not use "family size" or a mix that yields enough for a 9-by-13-inch pan.