Preheat the oven to 350°F. Grease an 8.5"x4.5" loaf pan with butter or oil.
In a large mixing bowl, beat together the butter, cooking oil, granulated sugar, and brown sugar until light and creamy.
Mash the bananas well. Add them to the bowl along with the eggs and vanilla extract. Beat again until smooth.
In a separate bowl, whisk together the flour, baking soda, salt, nutmeg, and cinnamon.
Add the dry ingredients to the wet ingredients and gently fold until just combined. Do not overmix the Homemade Banana Bread batter.
Fold in the chopped walnuts if using.
Pour the batter into the prepared loaf pan and smooth the top evenly.
Bake for 60 minutes or until the loaf is golden brown and a toothpick inserted in the center comes out clean.
Let the banana bread cool in the pan for 5 minutes, then transfer to a wire rack to cool completely before slicing.