Take the remaining tablespoon of butter and use it to coat a 9-by-5-inch loaf pan with a paper towel all over the bottom and sides. Line the pan with parchment paper: Use a piece of parchment paper a little narrower than the width of the loaf pan, and lay it across the bottom and up the sides of the pan, folding any extra over the edges (trim if necessary). This will help when you remove the loaf out later.
Bake until a toothpick or cake tester inserted into the center of the banana bread comes out clean, 50 minutes to 1 hour. Let it fully cool and set before cutting into it, about 1 to 2 hours. Slice and serve.
