In a large bowl, mix together the cocoa powder, granulated sugar, and vegetable oil until well combined.
Beat in eggs one at a time, then add vanilla extract.
In a separate bowl, whisk together flour, baking powder, and salt. Gradually stir the dry ingredients into the chocolate mixture until just combined.
Cover the dough and refrigerate for at least 3 hours or overnight. This step is important—the dough needs to be firm!
When ready to bake, preheat oven to 350°F and line baking sheets with parchment paper.
Place powdered sugar in a small bowl. Roll the chilled dough into 1-inch balls, then roll each ball generously in powdered sugar until completely coated.
Place cookies 2 inches apart on prepared baking sheets. Bake for 10-12 minutes. The cookies will spread and crack beautifully!
Let cookies cool on the baking sheet for 5 minutes before transferring to a wire rack. They'll firm up as they cool.