In a mug, combine cake mix with cocoa powder and mix well. Add mayo, egg, and water; stir well to combine. Mix in the chocolate chips
Put the mug into the microwave and cook on high for 1 minute to 1 minute and 20 seconds, until the cake is firm but still glossy. If you're using a large mug, you may need to cook for a few more seconds.
Top as desired and enjoy.
NOTE: if you do not have a boxed keto cake mix, stir together 2 tablespoons of almond flour, 1 tablespoon of 1:1 granulated sweetener, ΒΌ teaspoon of baking powder, and a pinch of salt. Mix together, then proceed with Step 1.