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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.
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In a microwave-safe bowl, or in a saucepan set over low heat, melt the butter.
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Add the sugar, stirring to combine. Remove from heat.
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Stir in the cocoa, espresso powder, salt, baking powder, and vanilla.
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Whisk in the eggs, stirring until smooth.
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Add the flour, chips, and nuts, again stirring until smooth.
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Spoon the batter into the prepared pan.
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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.
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Remove the brownies from the oven, and cool for at least 1 hour before cutting.
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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.
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Just before serving, garnish the brownies with whipped cream, shaved chocolate, and a dusting of espresso powder.