Instructions

In a small bowl, whisk together flour, sugar, baking powder, and cinnamon until thoroughly, completely combined, with no streaks of any ingredients remaining. Blend in milk, butter, and vanilla until batter is smooth. Into a 14-ounce (or larger) microwave-safe mug with straight sides, scoop a big spoonful of batter, then sprinkle with a spoonful of cinnamon sugar. Alternate layers, ending with cinnamon sugar.
Microwave on high for 1 to 1 1/2 minutes, or until cake is done to your liking. Allow to cool for a couple of minutes before serving.