Spray the inside of a 12oz (or larger is preferred) mug with non-stick cooking spray.
Fill the mug with 10 tablespoons of your favorite flavor cake mix.
Pour in 7 tablespoons of milk.
Pour in 1 teaspoon of oil.
Mix well with spoon or whisk until smooth. The batter should be a bit thin. Add additional tablespoons of milk if necessary.
Heat in the microwave on high for 2 minutes. Cake will pull away from the sides of the mug as it cooks. If your mug cake is still liquid in the center, add 30 second increments until desired doneness.
Caution the mug and the cake will be HOT. Using oven mitts to remove the mug is strongly advised.
Allow to cool for 1 minute or until the mug is comfortable to handle.
Decorate with sprinkles, frosting, or anything else you like.