Step 1

Whisk together flour, sugar, cocoa powder, baking soda, and salt in a mug or small bowl.

Step 2

Add water, oil, vinegar, and vanilla extract and stir until smooth.

Step 3

Spray a mug or small ramekin with nonstick cooking spray. Add the cake batter.

Step 4

Cook in microwave on 70% power for 40-60 seconds. This will depend on your microwave, but mine took 45 seconds. A toothpick will come out clean from the center when it's done.

Step 5

Let cool for at least 10 minutes before eating. Top with a dusting of powdered sugar or whipped topping.