Mix the cocoa powder, flour, baking powder and salt together in a medium bowl and set aside.
Using an electric mixer, mix the butter, sugar and vanilla in a large bowl and beat until combined. One at a time, add in the eggs and mix on low to medium speed until just combined.
Add the dry ingredients from the medium bowl to the large bowl and mix on a low speed until all mixed together.
Cover the bowl and chill the dough for an hour, up to overnight, depending on how thick you want your cookies. The longer you chill the dough, the thicker they’ll be.
Preheat oven to 350F/177C. Place the powdered sugar in a medium bowl and roll the dough out into balls about the size of a tablespoon and cover them well with the powdered sugar.
Line your baking sheets with parchment paper and place cookies on them and bake for 10-15 minutes, or until they spread out and start cracking. The cookies should still be soft, so make sure you let them cool on the sheet for 5 minutes before moving them your cooling rack to finish cooling.