Preheat oven to 375ºF, and grease a 9 x 5-inch loaf pan. 

In a large bowl, use a hand mixer to beat together butter and sugar until light and fluffy (about 3 minutes). 

Add the eggs and vanilla, and continue mixing until fully incorporated.

Next, add the bananas and mix until smooth and no chunks remain.

Last, add the baking soda, salt, cinnamon, nutmeg, and flour. Mix until everything is just combined without over mixing. 

Stir in walnuts or pecans if using.

Pour the batter into the prepared loaf pan and bake for 15 minutes. Then reduce the temperature to 350ºF. Bake for an additional 45 minutes or until a toothpick inserted in the center comes out clean. If the bread appears to be browning quickly, make a foil tent to cover it during the last 20-30 minutes of baking.

Remove from the oven and allow to cool completely before slicing.