In a small bowl mix the flour, sugar, baking powder, cinnamon, cream of tartar, and salt.
1/4 cup all-purpose flour, 2 tbsp sugar, 1/4 tsp baking powder, 1/4 tsp ground cinnamon, Pinch of cream of tartar, Pinch of salt
Mix in the milk, melted butter, and vanilla extract until batter forms.
2 tbsp milk, 1 & 1/2 tbsp unsalted butter, 1/2 tsp vanilla extract
In a small bowl, mix the sugar and cinnamon for the topping.
1/2 tbsp sugar, 1/4 tsp ground cinnamon
Add a spoonful of the cake batter into a lightly greased mug, sprinkle with the cinnamon sugar, repeat the process until you are done with the cake batter. Make sure to finish with a generous layer of cinnamon sugar.
Microwave on high for 1 to 1 1/2 minutes. Start checking at the 1-minute mark to avoid overcooking. The cake should rise and be slightly springy to the touch.
Cool slightly and enjoy!