Melt butter and chocolate in a saucepan over low heat. Don't turn the heat up, as the chocolate can burn! Once melted set it aside. In a mixing bowl, whisk together the sugar, eggs, vanilla, peppermint extract, instant coffee, baking powder, and salt until smooth. Pour in the melted chocolate and butter mixture and whisk until well combined. Add the flour and fold the flour in until it's incorporated. The batter is going to be super liquid-y, don't worry! Cover and refrigerate for at least 2-3 hours, but overnight is best. When ready to bake, preheat the oven to 325°F. Line a baking sheet pan with parchment paper or a silicone mat. Divide the cookie dough into 12 equal portions, about 45 g each. Roll each portion into a ball and roll the ball in powdered sugar, coating it VERY well. Place the cookies 2-3 inches apart on the prepared baking sheet pan. Bake the cookies for 10-12 minutes and cool the cookies on the tray before moving them to a rack to cool completely.