Line a baking sheet with parchment paper.

In a medium bowl, whisk together the flour, cocoa powder, baking powder, salt, and espresso powder (if using).

In a stand mixer fitted with the paddle attachment, cream together the butter, sugar, and vanilla on medium speed until light and fluffy, about 2 minutes. Scrape down the sides of the bowl with a rubber spatula. Mix in the egg until well incorporated. Scrape down the bowl again.

Add the flour mixture all at once and mix on low speed just until it all comes together. Scrape down the bowl. Turn the speed to medium and mix for 15 seconds. Turn the speed down to low, add the chopped chocolate (if using), and mix until just incorporated.

Scoop the cookie dough using a #70 (1-tablespoon) portion scoop onto the prepared baking sheets. Roll each dough ball in the palm of your hand to make a round sphere. Roll the cookies in granulated sugar. There the dough balls for about 15 minutes (they should be very cold, but not frozen solid) or refrigerate for at least 30 minutes.

Preheat the oven to 375°F. Line two baking sheets with parchment paper.

Dip the cookies in the confectioners' sugar and place them onto the prepared baking sheets, leaving 3 inches between each cookie. They will spread!

Bake, one sheet at a time, in the middle of the oven for 8 to 10 minutes, until the cookies puff up, the centers no longer look wet, and the sugar coating looks crinkled. Don't overbake the cookies, or they will become crispy.

Cool completely on the baking sheet before moving.