Melt coconut oil in a microwave-safe mug or ramekin. Then add heavy whipping cream, lemon extract, and the egg. Whisk until yolk is incorporated and mixture is well-combined.
In a small bowl, combine coconut flour, chia seeds, erythritol, and baking powder. Mix thoroughly to combine.
Add dry ingredients to the mug (or ramekin), then mix thoroughly until well-combined.
Place in the microwave for 50 to 90 seconds on high, being careful not to overcook. Check at 50 seconds and again at 10-15 second increments to ensure you remove it at the right time.
When finished, put a fork in the mug cake and carefully lift it up and flip it over. If the bottom isn’t fully cooked yet (this will depend on your microwave), cook it for another few seconds.
Make Glaze Icing and drizzle on top.
Your mug cake can be enjoyed in the mug, fully intact on a plate or bowl, or cut in half on a plate or bowl.