Lightly coat a 12-ounce microwave-safe mug with nonstick cooking spray.
Add the cake mix, water, and applesauce to the mug. Stir until smooth, making sure there are no dry pockets of cake mix at the bottom or along the sides of the mug.
Microwave on high for 60 to 90 seconds, depending on the power of your microwave. The cake is done when the center is set and springs back lightly when touched.
Allow the mug cake to cool for 1 to 2 minutes before serving.
Notes
Use a mug that holds at least 12 ounces to give the cake room to rise. Stir thoroughly. Any dry cake mix left in the mug will create pockets of uncooked batter.
Microwave wattages vary. Start with 60 seconds and add additional time in 10-second increments if needed.
Chocolate, vanilla, lemon, spice, and funfetti cake mixes all work well in this recipe.
For an extra treat, top the warm cake with whipped topping, ice cream, chocolate chips, or sprinkles.
This mug cake is best enjoyed immediately after cooking.