In a microwave-safe mug (that can hold at least 12 oz of liquid), add all ingredients. Mix with a small whisk until batter is smooth and completely combined with no egg streaks remaining.
Cook cake in the microwave at full power for about 1 minute. Be careful to not overcook the cake because that will cause the cake to be dry when it cools. Allow the cake to cool a few minutes before eating. The cake is a little plain on its own, so I recommend topping with a sugar-free chocolate spread or syrup or sugar-free Nutella spread.
Notes
I use an 1100 watt microwave. You may need to adjust time and/or power if you are using a different wattage.
I topped my cake with sugar-free chocolate spread. You can also use sugar-free chocolate syrup or sugar-free Nutella spread.
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The estimated nutrition carbohydrates count excludes sugar alcohols. The net carbs excludes both fiber and sugar alcohols.
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.