Combine all ingredients except streusel ingredients into an oversized mug. Stir with a small whisk or fork until batter is smooth. Make sure your mug is very big or else the streusel will slide right out during cooking. You can divide batter into two mugs, but then I recommend doubling the streusel recipe.
Make streusel in small bowl with fork until butter is mixed with the flour and sugar and resembles a coarse topping.
Cook in microwave for about 1 1/2 minutes.
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.