In a large mixing bowl, whisk together the unsweetened cocoa powder, granulated sugar, and vegetable oil. The mixture will look thick and gritty.
Whisk the eggs into the chocolate mixture one at a time, ensuring each is fully incorporated before adding the next. Whisk in the vanilla extract until the batter is smooth and glossy.
In a separate, smaller bowl, whisk together the all-purpose flour, baking powder, and salt.
Pour the dry flour mixture into the wet chocolate mixture. Use a rubber spatula to fold them together just until no dry flour streaks remain. Do not overmix.
Cover the bowl tightly with plastic wrap and chill the dough in the refrigerator for at least 2 hours (the dough will be extremely sticky before chilling).
Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper. Pour the powdered sugar into a wide, shallow bowl.
Use a cookie scoop to portion the chilled dough into 1-inch balls. Drop them directly into the powdered sugar and roll them until heavily and completely coated.
Place the coated dough balls onto the prepared baking sheets, spacing them about 2 inches apart.
Bake for 10-12 minutes, or until the edges are set and the tops have cracked, but the centers still appear slightly soft.
Allow the cookies to cool on the hot baking sheets for 5 minutes before transferring them to a wire rack to cool completely.