Preheat the oven to 350°F (175°C). Grease or line a 9x5-inch loaf pan with parchment paper.
In a large bowl, mash the ripe bananas until smooth using a fork or potato masher.
Stir in melted butter and sugar until combined. Beat in eggs one at a time, then mix in vanilla extract.
In a separate bowl, whisk together flour, baking soda, salt, cinnamon, and nutmeg.
Gently fold the dry ingredients into the banana mixture until just combined—don’t overmix.
Fold in chopped walnuts or pecans if using.
Pour the batter into the prepared pan and smooth the top. Bake for 55–65 minutes, or until a toothpick inserted in the center comes out clean.
Cool the bread in the pan for 10 minutes before transferring to a cooling rack. Slice when fully cooled.