Preheat oven to 350°F and spray 9x13 baking dish with nonstick cooking spray
In a microwave safe dish melt the butter. Microwave for 30 seconds, stir, and repeat until the butter is completely melted.
¾ cup + 3 tbs unsalted butter
Stir cocoa powder into melted butter making sure there are no clumps. Set aside.
¾ cup dark cocoa powder*
While butter mixture is cooling, in a separate small bowl combine the flour, baking powder, and salt. Set aside.
1 cup all purpose flour, ½ teaspoon baking powder, ¼ teaspoon salt
In a stand mixer, or using a hand mixer, mix together the butter mixture (it’s okay if it’s still warm), sugar, espresso powder, and vanilla. Then add the eggs one at a time, letting each egg become fully incorporated into the batter before adding the next.
2 cups sugar, 1 teaspoon espresso powder optional, 4 large eggs, 1 teaspoon vanilla
By hand, with a large rubber spatula or mixing spoon, fold in the flour mixture. Folding in the flour will help the brownie batter keep the air in it.
Fold in the chocolate chips.
1 cup milk chocolate chips*
Reserve 1 cup of batter, then pour remaining batter into prepared baking dish.