Preheat the oven to 350°F. Lightly grease a 10" x 15" jelly roll pan or a 9" x 13" pan. For guaranteed easy removal of the brownies, line the greased pan with parchment, and grease the parchment.
1) In a microwave-safe bowl, or in a saucepan set over low heat, melt the butter.
2) Add the sugar, stirring to combine. Remove from heat.
3) Stir in the cocoa, espresso powder, salt, baking powder, and vanilla.
4) Whisk in the eggs, stirring until smooth.
5) Add the flour, chips, and optional nuts, again stirring until smooth.
6) Spoon the batter into the prepared pan.
7) Bake the brownies for 28 to 34 minutes, until a cake tester inserted into the center comes out clean. The brownies should feel set on the edges, and barely set in the center.
8) Remove the brownies from the oven, and cool for at least 1 hour before cutting.
9) Use a 1 1/2" round cutter to cut as many circles as possible (about 46) out of the brownies in a 10" x 15" pan. You'll get about 38 from a 9" x 13" pan. Wrap well; enjoy the leftover scraps.
10) Just before serving, garnish the brownies with whipped cream, shaved chocolate, and a dusting of espresso powder.