Whisk together flour, sugar, baking powder, cinnamon and salt in 16-ounce mug. Place butter in a microwave-safe bowl and set onto glass turntable in microwave. Press “+30 Sec” to melt butter. If butter isn’t melted after 30 seconds, repeat.
Once butter is melted, stir in milk and vanilla. Add dry ingredients to wet ingredients and stir until batter is combined and no dry spots remain. Transfer half of batter to mug. Whisk together cinnamon sugar topping and sprinkle half of the mixture on top of the batter in the mug. Pour remaining batter into mug and top with remaining cinnamon sugar.
Place mug onto glass turntable. Press “+1 MIN” twice to set cook time. Press “Start” to cook cake. Serve immediately.
