Grease a microwave-safe coffee mug. Set aside.
In a small bowl, whisk the egg just until the yolk and white are blended. Add the heavy cream, melted butter, and vanilla. Mix well.
Next, add the dry ingredients to the wet mixture. Add the unsweetened cocoa powder, sweetener, salt and baking powder. Whisk until well blended.
Carefully pour the cake batter into the greased coffee-mug. Microwave for 1 minute and 30 seconds. The cake will have a lava cake-like consistency in the center. Microwave the cake for 2 minutes if you prefer a more cakey texture.
Make your keto mug cake a little sweeter with the addition of a light drizzle of sugar-free chocolate syrup.
Top your mug cake with Lily's keto-friendly chocolate chips for an added indulgence
Blend in your favorite choice of sugar-free peanut butter powder for an out-of-this-world peanut butter twist on this fudgy guilt-free treat.