In a large bowl, beat granulated sugar, brown sugar, cocoa powder, and vegetable oil until the mixture is smooth. Add the eggs one at a time, mixing well after each addition, then stir in the vanilla extract.

In a separate bowl, whisk together the all-purpose flour, baking powder, and salt. Gently fold the dry ingredients into the wet mixture until just combined.

Cover the bowl with plastic wrap and refrigerate the dough for at least 4 hours, or overnight, to help it firm up for shaping.

Preheat your oven to 350°F. Line baking sheets with parchment paper. Scoop 1-inch portions of chilled dough using a small ice cream scoop or tablespoon, then roll each ball in powdered sugar until well coated. Place the balls on the baking sheet about 2 inches apart.

Bake for 10 to 12 minutes, until the edges are firm and the tops crackle. Allow the cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.