In a microwave-safe bowl, melt the butter in 20 - 30 second increments. When the butter is warm and mostly melted, remove from microwave, and add chopped chocolate. Stir until chocolate is melted, and it is smooth and glossy. Set aside.

In the bowl of a stand mixer, fitted with the paddle attachment (or in a mixing bowl, using a handheld electric mixer), combine the cocoa powder, both sugars, and the butter/chocolate mixture. *Sift cocoa powder to avoid lumps.

Add the eggs, one at a time, beating after each addition until fully incorporated. Then add vanilla and beat again to mix thoroughly.

In a small mixing bowl, whisk together the flour, baking powder, salt and espresso powder.

Add flour mixture to the butter and cocoa mixture, beating on low, just until combined. Use a sturdy rubber spatula to scrape down the sides and bottom of the bowl to make sure everything is combined.

Wrap bowl tightly with plastic wrap and refrigerate at least 3 - 4 hours, or overnight.

Line 2 cookie sheets with parchment paper and preheat the oven to 350°F / 325° convection / 180°C / Gas mark 4.

In 2 small bowls, place powdered sugar in one and 4 tbsp. granulated sugar in the other.

Using a tablespoon, or a small cookie scoop, scoop out tablespoon size portions of dough and roll them into balls with your hands. Drop them into the granulated sugar, toss to coat, then roll them in powdered sugar. Place on lined baking sheet, leaving 2 inches between each cookie. (I bake 12 at a time)

Bake for 12 minutes. Cool on the cookie sheet for 2 - 3 minutes before transferring to a wire rack to cool completely. Repeat until all of the cookie dough is used up.