-
Melt bittersweet chocolate chips and butter in a heavy saucepan over low heat, stirring constantly until melted and well-combined.
-
Remove from heat, and set aside.
-
In the bowl of a stand mixer, beat the eggs, sugars, vanilla, baking powder, and salt on high speed 5 minutes, or until the batter is thick and creamy. This step is key, so make sure to beat the mixture for the full 5 minutes.
-
Reduce the speed to low, and mix in the melted chocolate until well-combined.
-
Stir in flour and cocoa powder just until combined.
-
Add nuts, if using, and mini chocolate chips. Stir in to combine. The batter should be the consistency of a thick brownie batter at this point.
-
Cover the batter, and chill for 30 minutes.
-
Preheat oven to 350 F. Line two baking sheets with parchment paper.