In a microwave-safe mug, beat the egg and combine with melted butter, vanilla extract and a pinch of salt. Whisk until combined.
Once smooth, add almond flour, keto granular sweetener and baking powder. Mix all ingredients until you get a smooth mug cake batter. Optionally, fold through chocolate chips.
Place the mug in the microwave and cook on high for approximately 45 seconds to 1 minute, or until the cake has risen and is set in the center. Microwaves may vary, so adjust the cooking time accordingly.
Carefully remove the mug from the microwave (it will be hot!) and allow the cake to cool for a minute before serving.