A mug cake is a single-serving cake mixed and cooked directly in a microwave-safe mug, ready in a few minutes without an oven.
Dry ingredients such as flour, sugar, baking powder, and flavorings are combined in the mug, then wet ingredients like milk, oil, and sometimes egg are stirred in to form a batter; the mug is microwaved, typically for 1-2 minutes, until the cake is set and risen. Because there is very little batter and no crust to develop, texture is denser and moister than an oven-baked cake, and results vary more by microwave wattage than with conventional baking.
Mug cakes are easy to customize with mix-ins and flavorings, from chocolate and vanilla to savory versions with cheese or bacon, and are often used to test a flavor combination on a small scale before baking a full-sized cake.