Make the cookie dough: combine the melted butter and both sugars. Add in the egg and vanilla and mix. Fold in the flour and baking powder. Then finally, add the chopped chocolate pieces.
Randomly place pieces of the dough over the brownies, so the chocolate brownie batter is not entirely covered (I like the marbled look).
Bake for 30-35 minutes, until golden brown! Let cool before slicing and serving.