Mix cocoa powder, granulated sugar, and oil in a large bowl until glossy.
Beat in eggs one at a time, then add vanilla extract.
In another bowl, whisk together flour, baking powder, and salt.
Gradually fold the dry ingredients into the cocoa mixture.
Chill the dough in the fridge for at least 4 hours or overnight.
Roll chilled dough into balls and coat in powdered sugar.
Place dough balls on parchment-lined baking sheets spaced 2 inches apart.
Bake at 350ºF (175ºC) for 10–12 minutes. Cool on sheet before transferring to wire racks.
Notes
Store cooled cookies in an airtight container at room temperature for 3–4 days or freeze for long-term storage. Add a slice of bread to container for extra moisture.