Preheat the oven to 375°F and line a baking sheet with a silicon mat or parchment paper.
In the bowl of a stand mixer fitted with the paddle attachment, cream the butter and sugar together on high until light and fluffy - about 2 minutes.
Add in the egg and vanilla extract. Mix until combined.
Add the cocoa powder and beat on medium speed until combined.
Turn the mixer off and add the flour, baking powder, and salt. Mix on low speed until just combined.
Roll out the dough on a lightly floured surface and cut into circles. Transfer them to the prepared baking sheet. Make sure you do not crowd the baking sheet.
Bake cookies 7-8 minutes. Let them cool 5 minutes on the baking sheet before transferring to a wire rack to cool completely.