Mix the topping ingredients together to create cinnamon sugar.
In a small bowl, whisk together flour, brown sugar, 1 tablespoon granulated sugar, the baking powder, and 1/4 teaspoon cinnamon until thoroughly combined.
Blend in milk, oil, and vanilla extract until the batter is smooth.
In a large microwave-safe mug, layer half of the batter, followed by half of the cinnamon sugar. Repeat with the remaining batter and the sugar mixture.
Microwave on high for 1.5-2 minutes or until the cake is cooked. Cooking time will vary depending on your microwave and mug. Allow to cool for a few minutes before serving.