Preheat oven to 350°F. Grease an 8½ x 4½-inch loaf pan and set aside.
In a medium bowl, sift or whisk together flour, nutmeg, cinnamon, baking soda and salt. Set aside.
In a separate large bowl, whisk together mashed banana, melted butter, sugar, egg and vanilla extract.
Gradually add the dry ingredients to the wet ingredients, stirring just until combined. Fold in the walnuts.
Pour batter into prepared loaf pan. Bake until the bread is golden brown and a toothpick inserted in the center comes out clean, about 50-60 minutes. Do not overbake.
Remove from the oven, unmold from the pan, and cool completely on a wire rack before slicing and serving.
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Notes
Make-Ahead: This bread just gets better as it sits! The flavors come together and the bananas help to keep the bread nice and moist.
How to Store: Always wrap your loaf in plastic wrap or foil to prevent it from drying out. It does not need to be refrigerated. The bread will stay fresh at room temperature on the counter for 2-3 days, and it will last in the refrigerator for up to 1 week.
How to Freeze: Cool the loaf completely, wrap tightly, and freeze for up to 3 months.
How to Ripen Bananas in the Oven: Want to make this bread right away, but your bananas aren't ripe yet? You can ripen the bananas in the oven! To do so, preheat the oven to 300°F. Place bananas (in their peels) on a foil-lined baking sheet. Bake for 30-45 minutes, or until mushy and sweet. The banana peels will turn a black, shiny color (and look really weird!), but don't worry -- the insides will be perfect. In fact, they're so soft, that you probably won't even need to mash them with a fork. Allow the banana cool completely before using in the recipe.