In a microwave-safe mug, whisk together the egg, almond flour, coconut flour, erythritol, baking powder, and cinnamon.
Add the melted butter and vanilla extract, and whisk until well combined.
Add the cream cheese to the center of the mixture, pressing down slightly.
Microwave on high for 60-90 seconds, until the cake is cooked through.
Let cool for a minute or two, and then enjoy!