Melt chocolate in a heat-proof bowl over a pot of simmering water (or using a double boiler), stirring frequently.
In a small bowl, mix together flour, baking powder, and cocoa.
In a medium bowl, whisk together sugar, eggs and butter. Gradually whisk in melted chocolate and mint extract, until smooth. Fold in flour mixture until combined. Refrigerate until firm, at least 3 hours to overnight.
Preheat oven to 325 degrees. Roll tablespoons of dough into balls, then roll in confectioners' sugar to coat. Transfer to parchment-lined baking sheets, spacing each 1 inch apart. Bake for about 15 minutes, or until slightly firm in center.
Let cool slightly on cookie sheets for 5 minutes and then transfer cookies to wire racks to cool completely.
Recipe by Alida's Kitchen at https://www.alidaskitchen.com/2011/12/21/chocolate-mint-crackle-cookies/