Preheat oven to 350°F. Lightly grease sides of an 8x8-inch baking pan and line with parchment paper, slightly overhanging two edges.
For the cookie dough: In a large bowl, cream butter and sugars. Lightly mix in egg and vanilla. Add baking soda, baking powder, salt and flour, mixing well until no streaks remain. Finally, add chocolate chips and mix until dispersed throughout. Set aside.
For the brownie batter: Melt butter and chocolate in a double boiler, set over a saucepan with simmering water. Stirring gently until completely melted and smooth. Remove from heat, whisk in sugar, followed by egg and vanilla. Whisk in cocoa and salt. Gently fold in all flour until combined.
Pour brownie batter into prepared pan, spreading out evenly with an offset spatula. Top off with large spoonfuls of cookie dough, press down gently. Bake for 25-30 minutes.
Cool in pan completely before slicing. Store in an airtight container.
Nutritional information is provided as a courtesy and is an estimate only. Nutrition information can vary for a variety of reasons. For the most accurate data, use your preferred nutrition calculator with the actual ingredients you used to make this recipe.
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