- 1 egg
- 2 tablespoons all-purpose flour
- 2 teaspoons white sugar
- 1 1/2 teaspoons milk
- 1 teaspoon chopped rhubarb
- 1/3 teaspoon ground cinnamon
- Mix egg, flour, sugar, milk, rhubarb, and cinnamon together in a large microwave-safe mug.
- Cook on high until cake rises above the top of the mug, about 3 minutes. Let cool for 1 minute before serving.