Step 1

Preheat the oven to 350°F. Whisk together the cocoa powder, flour, granulated sugar, salt, baking soda, and baking powder in a 9-inch square cake pan.

Step 2

Add the water, oil, and vinegar to the pan, stirring gently to blend the wet ingredients into the dry. Scrape down the sides with a silicone spatula and bake until a cake tester inserted in the center comes out clean, about 30 minutes. Cool for 30 minutes before serving. Serve plain or dusted with powdered sugar.