Preheat the oven to 350°F (175°C). Grease a 9×5-inch loaf pan with butter or non-stick spray.
In a medium bowl, whisk together the all-purpose flour, baking soda, salt, ground cinnamon, and ground nutmeg until well combined.
In a large bowl, cream the softened unsalted butter and packed light brown sugar together until light and fluffy using a hand mixer or stand mixer.
Beat in the eggs one at a time, mixing well after each addition.
Add the pure vanilla extract and mix to combine.
Stir in the mashed ripe bananas until evenly incorporated.
Alternately add the flour mixture and buttermilk to the banana mixture, beginning and ending with the flour mixture. Mix just until combined; do not overmix.
Pour the batter into the prepared loaf pan and smooth the top with a spatula.
Bake in the preheated oven for 55 to 65 minutes, or until a toothpick inserted into the center comes out clean.
Remove the banana bread from the oven and let it cool in the pan for 10 minutes.
Transfer the bread to a wire rack to cool completely before slicing and serving.