The directions here are for making 2 mug cakes. You can easily halve the recipe if you just want to make one. Split the whisked egg evenly into two oversized microwave safe mugs (approximately 2 tbsp of whisked egg per mug). I used 12 oz mugs.
Add 1/4 cup + 1 tbsp of Nutella into each mug. Add 2 tbsp of flour into each mug. Mix with a sturdy whisk until batter is smooth. Batter will be very thick, so you will need to exert some power in your whisking.
Microwave each mug separately for about 1 minute. Allow the brownie to cool slightly before eating. If you want an extra chewy brownie texture, allow the brownie to fully cool (about 20-30 minutes). For a nicer presentation, I recommend removing cake from mug and placing into a smaller plate or ramekin and then topping with powdered sugar, fruit, or ice cream on top.
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.