In a large mixing bowl, whisk together the cocoa powder and 2 cups granulated sugar until no cocoa clumps remain. Add the oil and whisk until the mixture looks shiny and thick, like a chocolate paste. This helps “bloom” the cocoa for deeper flavor.

Add the eggs one at a time, whisking well after each addition until the batter is smooth and glossy. Whisk in the vanilla extract. The mixture should resemble thick brownie batter with no visible egg streaks.

In a separate medium bowl, whisk together the flour, baking powder, salt, and instant espresso powder (if using) until evenly combined.

Switch to a wooden spoon or sturdy spatula. Add the dry ingredients to the cocoa mixture in 2–3 additions, stirring gently after each. The mixture will quickly become a very thick, sticky dough. Scrape down the sides and bottom of the bowl to ensure no dry spots remain.

Cover the bowl tightly with plastic wrap or a reusable cover and refrigerate for at least 2 hours and up to 24 hours, until the dough is firm enough to scoop and roll. If your fridge is very cold, let the dough sit at room temperature for 5–10 minutes before scooping.

When ready to bake, preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper or silicone baking mats. Place 1/4 cup granulated sugar in one shallow bowl and the powdered sugar in another to create a rolling station.

Using a small cookie scoop (about 1 to 1.5 tablespoons) or a spoon, scoop portions of dough and roll quickly between your palms to form smooth balls. If the dough is too sticky to handle, return it to the refrigerator for 10–15 minutes.

Roll each dough ball first in the granulated sugar to coat completely, then roll generously in powdered sugar to create a thick, even layer. Place the coated balls on the prepared baking sheets, spacing them about 2 inches apart.

Bake one sheet at a time for 10–12 minutes, or until the cookies are puffed, the tops are well crackled, and the edges look just set. The centers should still appear slightly soft and a bit underdone for a fudgy texture.

Let the cookies cool on the baking sheet for 5 minutes to firm up, then transfer to a wire rack to cool completely. The powdered sugar will set into the cracks. Enjoy slightly warm or at room temperature.