Choose the right mug: Use a microwave-safe mug that holds at least 12 ounces. This gives the cake room to rise without overflowing.

Mash the banana: Peel and add the banana to the mug. Mash with a fork until mostly smooth with a few small lumps.

Add wet ingredients: Stir in the milk, oil, and vanilla until the mixture looks creamy and well combined.

Add dry ingredients: Sprinkle in the flour, sugar, baking powder, and salt. Fold gently with the fork just until no dry streaks remain. Do not overmix.

Stir in extras: If using chocolate chips, nuts, or cinnamon, fold them in now. Smooth the top.

Microwave: Cook on High for 60–90 seconds, depending on your microwave’s power. Start at 70 seconds and check. The cake should look set on top and spring back lightly when touched. If it’s wet in the center, cook in 10–15 second bursts.

Rest briefly: Let the mug cake sit for 1–2 minutes. It finishes setting and becomes fluffier.

Finish and serve: Add your favorite topping and enjoy warm straight from the mug.