Preheat the oven to 375 degrees F. Line two baking sheets with parchment paper and set aside.
Sift the cocoa powder into the flour (to avoid lumps) and then whisk in the baking powder, salt and espresso powder (if using).
In a stand mixer with the paddle attachment (or a hand mixer), mix the butter and sugar on medium high speed until evenly combined. Add the egg, chocolate liqueur and vanilla and mix on medium speed until just combined. Add the flour mixture and mix until just combined. Stir in the chocolate chips by hand.
Use a 1-tablespoon cookie scoop to evenly portion out the cookie dough on the reserved baking sheets. Chill the cookie dough for 15 minutes or more. Bake for 12 minutes, preferably one sheet at a time on the middle rack, and allow to cool for several minutes before serving.
Notes: Use a 1 tablespoon scoop for approximately 48 cookies or a 2 tablespoon scoop for 24 larger cookies. All of the brand suggestions are optional. A cocoa powder other than Valrhona might result in a cookie that's lighter in color than what is seen in the photographs.