1/4cupunsweetened cocoa powder not Dutch-processed
1/2cupmini semisweet chocolate chips
Preheat oven to 375 F. Grease and flour a 12-cup muffin tin. Set aside. Make sure you really grease the muffin tin so that the brownies don't stick.
Melt chocolate 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, and salt on high speed 5 minutes, or until the batter is thick and creamy.
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 chocolate chips. Stir in to combine. The batter should be the consistency of a thick brownie batter at this point.
Divide batter among muffin cups. They should be about 3/4 full.
Bake 15-25 minutes. The brownies will be puffed and the top should be shiny and cracked. Bake toward the lower end of the baking time if you want fudgier middles and longer if you want a cakier brownie.
Let cool in muffin tin for 10 minutes, and then remove to a wire rack to finish cooling.