In a large microwave-safe mug, whisk together the almond flour, cocoa powder, granulated erythritol, and baking powder.
Add the egg, melted butter, heavy cream, red food coloring, and vanilla extract. Stir vigorously with a fork until the batter is completely smooth with no lumps.
Microwave on high for 70 to 90 seconds until the cake is set on top but still slightly moist. Let it rest for 1 minute.
While the cake rests, mix together the softened cream cheese and powdered erythritol with a fork until smooth and creamy.
Top the warm mug cake with the cream cheese frosting and serve immediately.