Grease the inside of your microwave-safe mug with a little butter, coconut oil or ghee (to prevent sticking).
Add all of the ingredients in a small bowl and whisk to combine. Transfer the mixed ingredients to your prepared mug.
Microwave for 1 minute. Use a toothpick or a knife to check that the mug cake is cooked all the way through (it should come out clean). If not, cook for another 20 seconds, or until done.
Remove and allow to cool for 5 minutes.
Optional to top with drizzled chocolate.
Notes
If using an oven, preheat oven to 350°F and bake in about a 3.5 inch ramekin (to ensure it's oven safe) for 25 to 30 minutes. Remove and allow to cool for about 3 to 5 minutes before adding the toppings.