Preheat and prepare: Heat the oven to 350°F (175°C). Line two baking sheets with parchment paper or silicone mats.

Whisk dry ingredients: In a bowl, whisk cocoa powder, cornstarch, baking powder, and salt until no lumps remain.

Beat egg whites and sugar: In a separate large bowl, whisk egg whites and sugar for 30–45 seconds until slightly thick and glossy. You don’t need stiff peaks—just a bit of volume.

Add flavor: Whisk in vanilla.

Mix in Nutella: Add Nutella to the egg white mixture and stir until mostly combined.

Combine: Add the dry ingredients and fold until you get a thick, shiny batter. It should be scoopable, like brownie batter. Fold in chocolate chips if using.

Scoop: Using a tablespoon or small cookie scoop, drop 1.5-tablespoon mounds onto the sheets, spacing about 2 inches apart. Smooth tops slightly with a damp finger for a neater look.

Bake: Bake 9–11 minutes, until tops are glossy and cracked and edges look set. Centers should still be soft.

Cool: Let cookies cool on the sheet for 10 minutes to firm up, then transfer to a rack. They will set as they cool.