1) Preheat the oven to 375°F. Lightly grease two baking sheets, or line with parchment.
2) Beat together the butter, sugars, cocoa powder, salt, baking soda, baking powder, and vanilla until well blended.
3) Add the egg, beating until smooth. Scrape the sides of the bowl, and beat again until smooth. If you're going to add chips, nuts, or dried fruit, beat in the 2 tablespoons milk; if you're going to bake plain cookies without add-ins, omit the milk.
4) Add the flour and espresso powder, mixing to combine.
5) Stir in the chips, nuts, etc., if you're using them.
6) Drop the cookies by the traditional "tablespoonful" (actually about 4 measuring teaspoons) onto the prepared baking sheets, spacing them about 2" apart. A tablespoon cookie scoop works well here.
8) Bake the cookies for 12 to 14 minutes, until they've lost their shiny appearance and look like they're set. Remove them from the oven, and cool right on the pans; or transfer to a rack to cool.
Yield: 1 1/2 to 2 1/2 dozen cookies, depending on add-ins.