Preheat the oven to 350°F (175°C). Grease a 9×5-inch loaf pan or line it with parchment paper.
In a medium bowl, whisk together the all-purpose flour, baking soda, salt, ground cinnamon, and ground nutmeg. Set aside.
In a large bowl, cream the softened unsalted butter and packed light brown sugar together until light and fluffy, about 3-4 minutes.
Beat in the eggs one at a time, mixing well after each addition.
Stir in the vanilla extract.
Mix in the mashed ripe bananas until combined.
Add the dry ingredients to the wet ingredients in two additions, alternating with the buttermilk, beginning and ending with the dry ingredients. Stir 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 allow it to cool in the pan for 10 minutes.
Transfer the bread to a wire rack to cool completely before slicing.