In a microwave-safe mug (8-10 ounces) add egg, butter, and vanilla extract. Whisk well using a spoon.
To the mug add all the dry ingredients almond flour, cocoa powder, coconut flour, baking powder, erythritol, cinnamon. Mix well to get rid of any lumps.
Microwave at full power for 45 seconds. Check and if required microwave again for 10 seconds more.
If making the chocolate drizzle, melt keto friendly chocolate in the microwave and drizzle on chocolate mug cake before serving.