In a microwave-safe mug, combine the all-purpose flour, granulated sugar, baking powder, and salt. Stir well to ensure there are no lumps.
Add in the milk, vegetable oil, and vanilla extract. Mix until the batter is smooth and well combined.
In a small bowl, create the cinnamon swirl by combining the brown sugar and ground cinnamon.
Pour half of the mug cake batter over to one side of the mug. Then, sprinkle the cinnamon-sugar mixture evenly on top.
Top with the remaining batter over the cinnamon mixture to encapsulate it.
Microwave on high for 1 minute and 30 seconds (microwave times may vary). The cake should rise and be set in the center; if it’s still wet, microwave in 15-second intervals until fully cooked.
Let the cake cool for a minute before adding cream cheese frosting on top, if desired.
Notes
Add cream cheese frosting on top for extra flavor.