Grease the inside of your microwave-safe mug with a little butter, coconut oil or ghee (to prevent sticking).
Combine all base ingredients in a small bowl or directly in your oven/microwave safe mug. If using a bowl, transfer the mixed ingredients to your 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 30 seconds, or until done.
Remove and allow to cool for 5 minutes.
Optional to top with whipped cream and pumpkin pie spice.
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.