Add egg to butter and whisk until air bubbles begin to appear.
Next, add in erythritol, cocoa powder, heavy cream, salt and vanilla extract, mixing until combined.
Using a microwave-safe mug, spray non-stick baking spray.
Pour in batter.
Place in microwave for 30-45 seconds. Every microwave is different. You want the outside of the cake slightly firm, while the middle is not yet set, that’s how you get the lava.
If you need more time in the microwave, set for 5-10 second intervals until you have the consistency of a Chocolate Lava Cake.
Plate and serve with Homemade Whipped Cream.