Using an electric mixer or a stand mixer, beat the butter and 1 cup of granulated sugar together until light and fluffy, about 3 minutes of mixing. 

Add the egg and the vanilla and mix until well incorporated. 

Add the flour, cocoa powder, baking powder, and salt to the bowl and mix on low until well combined and you have a uniform dough. Scrape down the sides of the bowl as needed to ensure the dough is mixed well. 

Roll 1.5 tablespoons of dough into balls. 

Roll each dough ball in granulated sugar and then powdered sugar until completely covered. The granulated sugar helps the powdered sugar to stick better.

Place the prepared dough on parchment or baking mat lined cookie sheets about 2 inches apart.

Bake until cookies about 1 minute after the point where they appear "cracked" and have start to spread, about 10-12 minutes total.

Let cookies cool on sheet pan for a few minutes, then transfer to a wire rack to cool completely.

Repeat with remaining cookie dough.

Store baked cookies in an airtight container for several days.