01 - Preheat oven to 350°F. Grease and flour a 9x5-inch loaf pan or line with parchment paper.
02 - Whisk together mashed bananas, eggs, melted butter, buttermilk, and vanilla extract in a large bowl until smooth.
03 - Combine flour, granulated sugar, brown sugar, baking soda, salt, and cinnamon in a separate bowl.
04 - Gently fold the dry ingredients into the wet mixture using a spatula. Stop when just combined to avoid overmixing.
05 - Fold in the chopped walnuts or pecans until evenly distributed throughout the batter.
06 - Pour the batter into the prepared loaf pan and smooth the top. Sprinkle extra nuts on top if desired.
07 - Bake for 50 to 60 minutes, or until a toothpick inserted in the center comes out clean or with just a few moist crumbs.
08 - Let the bread cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.