Step 1

Add melted butter and heavy cream to a microwave-safe mug. Whisk until fully combined.

Step 2

Add egg and whisk until batter is smooth. Make sure there are no egg white streaks.

Step 3

Add half of the cocoa powder. Whisk until cocoa powder is completely mixed into the batter and no lumps remain. Add in remaining cocoa powder and mix until batter is smooth. Batter should be getting thick.

Step 4

Add in erythritol. Whisk until evenly mixed into batter.

Step 5

Place chocolate squares onto the center of the batter and gently push in until they are just covered. Don't push too far because they will sink when the cake cooks.

Step 6

Cook cake in the microwave at full power for about 1 minute or until the middle of the cake puffs up, the cake has pulled away from the edges of the mug and is only slightly gooey around the edges.

Step 7

You can top the cake with ice cream, whipped cream, sugar-free syrup or powdered erythritol. Enjoy cake while still warm. The melted chocolate center will be closer to the bottom half of the cake. If you want easier access to the chocolate center, you can also flip the cake upside down onto a plate. This will also allow all the melted chocolate to pour over the cake. Enjoy the cake while it is still warm.