The dough is a bit sticky so make sure that it is well chilled. After rolling several balls of dough between the palms of your hand you will need to wash the residual chocolate off your hands, dry them thoroughly and then keep on rollin'. If I am making the whole batch all at once, I like to roll all the dough into balls first then roll them in the confectioners' sugar.
In a microwave safe bowl combine the unsweetened chocolate and the butter. Microwave for 1 minute then stir. Microwave for an additional 30 seconds or more until the chocolate and butter have completely melted. Set aside to cool slightly.
In a medium bowl, add the flour, cocoa, baking powder and salt. Whisk to combine. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment (or using a hand held mixer), beat the eggs, sugar, and vanilla until light in color, thick, and ribbons form, about 3 minutes on medium-high speed. Reduce the speed to low and slowly add the melted chocolate and butter. Beat until blended. Add the flour mixture and beat until blended. Fold in the mint chocolate chips. Cover the bowl with plastic wrap and refrigerate until the dough is firm enough to roll into balls, at least 3 hours.
Preheat the oven to 325º F (165º C). Line a baking sheet with parchment paper. Sift the confectioners' sugar into a small bowl.
Roll rounded tablespoons (I use a small ice cream scoop) into 1 1/4-inch balls. Roll each ball in the confectioners' sugar liberally to coat completely (do not shake off excess). Place the balls on the baking sheet, spaced 2 1/2-inches apart (1 dozen per baking sheet).
Bake the cookies until the tops are puffed and crinkled and the edges are slightly firm, 15-17 minutes. Let the cookies cool on the baking sheet for 5 minutes. Transfer the cookies to a wire rack to cool completely. Enjoy!