Melt 2 sticks of butter in a saucepan, add 2 1/4 cups sugar until sugar is dissolved. Remove from heat and add 1 teaspoon espresso powder, 1 1/4 cup cocoa powder, mix well. Add 4 eggs, one at a time and whisk vigorously until batter is smooth and shiny. Add 1 tablespoon vanilla, 1 teaspoon baking powder, 1 teaspoon salt and 1 1/2 cups flour and mix well (batter becomes very thick). Fold in 1 overflowing cup of chocolate chips and spread into greased 9×13 baking dish. Bake at 350 for 25-30 minutes. Let cool before cutting. Tip: score the top when warm to prevent the top crusty layer from cracking when you cut them once they're cool. This originated from King Arthur Flour online where I buy my dark cocoa. Bon Appetit!