Preheat your oven to 375°F (190°C) and line a 12-count muffin pan with liners.

Whisk together in a large bowl the all-purpose flour, baking soda, cinnamon, and salt until well combined.

Mix in another bowl the melted unsalted butter, light brown sugar, large egg, pure vanilla extract, and mashed ripe bananas until thoroughly combined.

Combine the wet and dry ingredients by gently folding them together until just mixed; some lumps are okay!

Distribute the batter evenly into the muffin liners, filling them about 2/3 full.

Bake for 16–20 minutes until a toothpick inserted into the center comes out clean.

Cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.