In a medium mixing bowl, whisk together the flour, cocoa powder, baking powder, and salt. Set aside.
In a separate large mixing bowl, whisk together the granulated sugar and melted butter until well combined.
Add the eggs, one at a time, beating well after each addition. Stir in the vanilla extract and peppermint extract.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix. The dough will be sticky.
Cover the dough with plastic wrap and refrigerate for at least 2 hours or overnight.
Preheat the oven to 350°F (175°C). Line a baking sheet with parchment paper.
Place the powdered sugar in a small bowl. Using a spoon or a cookie scoop, portion out small amounts of dough and roll them into balls using your hands.
Roll each dough ball in the powdered sugar until fully coated. Place the coated dough balls onto the prepared baking sheet, spacing them about 2 inches apart.
Bake for 10-12 minutes, or until the cookies have cracked on the surface. They will still be soft in the centre.
Allow the cookies to cool on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely.