Preheat the oven to 350 ℉.
In a double boiler (a metal bowl set on top of a small saucepan with water) add the chopped chocolate and unsalted butter and cook over medium heat until melted. Alternatively you can place the chocolate and butter in a microwave safe dish and microwave in 15 second intervals, stirring after each interval until the chocolate is melted and smooth.
In a large bowl whisk together flour, cocoa powder, baking powder, baking soda, salt and espresso powder (if using), set aside.
In a separate bowl whisk together granulated sugar, brown sugar, eggs until creamy. Added in the melted chocolate and peppermint extract and whisk until fully combined.
Add the flour mixture to the chocolate mixture and fold to combine.
Add the granulated sugar and powdered sugar each into their own shallow bowls or plates and line 2 baking sheets with parchment paper or a silicon baking mat.
Scoop out cookie dough using a a 1.5 oz cookie scoop and roll into a ball. Roll the cookie dough ball first in granulated sugar, and then in powdered sugar, making sure the cookie dough is thouroughly coated.
Place the cookies on the prepared baking sheet 2 inches apart. Bake for 12 minutes (rotating the pans halfway through, until the cookies are puffed and cracked on the top. Cool for 10 minutes on the baking sheets the transfer to a wire rack to cool completely.
Store cookies in an airtight container for up to 2 weeks.