In a bowl or a mug, melt the butter in the microwave.
Once melted, stir in mashed banana, brown sugar, milk, and vanilla. Stir well with a whisk or fork until thoroughly combined.
Add the flour, baking soda, cinnamon, and pinch of salt (about 1/4 teaspoon). Stir until well combined. Then, top with raisins and chopped nuts to taste.
Microwave for 1 minute to 1 1/2 minutes, depending on your microwave. Mine is perfect at about 1 minute. Let cool slightly before adding additional chopped bananas, raisins and nuts if preferred. An additional drizzle of melted butter is delicious, too, or a scoop of ice cream is approved!
Notes
What size mug do you need? I'm using a 14-ounce mug because it's my favorite. When in the microwave, the mug cake rises to the top before settling down once cooked. A 12-ounce mug should also work.Topping Ideas: Additional chopped bananas, raisins, and walnuts (or nuts) and a sprinkling of brown sugar (or coconut sugar). Or, vanilla ice cream is always delicious!