Add all ingredients except food coloring into an oversized microwave safe mug. Mix with a whisk until batter is smooth. Add in one drop of food coloring. Using a fork, gently swirl in a circular clockwise motion until red swirls form, but stopping before cake batter turns completely red.
Cook in the microwave for about 1 minute or until done. The cake is a bit plain, so I recommend that you serve it with whipped cream, Cool Whip, or a chocolate drizzle.
