Brown the butter. Melt butter in a light-colored saucepan over medium heat, swirling often. It'll foam, then turn golden, then amber with brown flecks and a nutty smell — about 5–7 minutes. Pour it into a bowl immediately to stop the cooking, and let it cool 10–15 minutes before using.

Mix the wet ingredients. Whisk the cooled brown butter with mashed banana and both sugars. Add eggs one at a time, then the vanilla.

Add the dry ingredients. Whisk flour, baking soda, salt, and cinnamon separately, then fold into the wet mixture just until no dry streaks remain. Over-mixing is the #1 cause of a dense, tough loaf — stop as soon as it's combined.

Bake. Pour into your prepared pan(s) and bake at 350°F until a toothpick comes out clean, about 55–65 minutes.

Cool completely before slicing. I know it's hard to wait, but slicing warm banana bread means it'll fall apart instead of holding a clean cut.