In a large microwave-safe mug, add all ingredients except Nutella. Mix with a small whisk until no lumps remain in the batter.
Add Nutella to a small bowl and heat up in the microwave for about 10-15 seconds to soften Nutella. Drop Nutella into the batter and swirl a few times with a fork. Place mug into microwave and cook at full power for about 1 minute and 15 seconds or until cake is done. Allow cake to cool a few minutes before eating.
The nutrition information provided are only estimates based on an online nutritional calculator. This is not a comprehensive list of all the nutrients in the recipe (i.e., does not include vitamins, cholesterol, etc). I am not a certified nutritionist. Please consult a nutritionist or doctor for accurate information and any dietary restrictions and concerns you may have.