Melt chocolate in a heatproof bowl set over a pan of simmering water, stirring.

Whisk together flour, baking powder and cocoa in a small bowl.

Whisk together granulated sugar, eggs and melted butter in a medium bowl. Gradually whisk in melted chocolate and mint extract until smooth. Stir in flour mixture. Refrigerate until firm, at least 3 hours.

Preheat oven to 325 F. Roll tablespoons of dough into balls using your palms, then roll in confectioners' sugar to coat. Transfer to parchment lined baking sheets, spacing each 1 inch apart. Bake until slightly firm in the center, about 15 minutes.

Let cool slightly on sheets set on wire racks. Transfer cookies to racks and let cool completely.

Dough can be refrigerated for up to 3 days or rolled into balls and frozen for up to 2 weeks. Roll in confectioners' sugar just before baking.

Store cookies at room temperature for up to 3 days.