In a bowl, mix cocoa, sugar, and oil. Beat in eggs one at a time, then vanilla.
In a separate bowl, whisk flour, baking powder, and salt. Gradually add to wet mixture.
Cover dough and chill for at least 2 hours or overnight.
Preheat oven to 350°F (175°C). Line baking sheets with parchment.
Roll chilled dough into 1-inch balls, then roll in powdered sugar.
Place on baking sheet 2 inches apart.
Bake for 10–12 minutes. Cookies will be soft but set as they cool.
Cool on the pan for 5 minutes, then transfer to a wire rack.