In a microwave-safe mug, combine the flour, granulated sugar, baking powder, and salt. Mix thoroughly to incorporate all dry ingredients.
Add the milk, vegetable oil, and vanilla extract to the dry mixture. Stir until a smooth batter forms.
In a small bowl, combine the cinnamon and brown sugar to create the cinnamon swirl mixture.
Pour half of the batter into the mug, followed by half of the cinnamon swirl mixture. Use a knife or a toothpick to gently swirl the mixture without fully mixing it in.
Pour the remaining batter on top, and then add the rest of the cinnamon swirl mixture. Again, gently swirl it with a knife.
Microwave the mug for 1 minute and 30 seconds, watching closely to avoid overflow. Cooking time may vary depending on the microwave’s wattage; if necessary, add an additional 15 seconds until the cake is set.
Once done, allow the mug cake to cool for a minute. Optionally drizzle with cream cheese icing for extra sweetness.
Notes
Optional cream cheese icing can be added for extra sweetness.