Preheat the oven to 350°F (175°C). Grease the bottom of a 9 x 5 x 3 inch loaf pan.

In a medium bowl, whisk together flour, baking soda, salt, baking powder, and cinnamon. Set aside.

In a mixing bowl, combine melted butter with granulated sugar and brown sugar. Mix on medium speed until smooth.

Beat in the eggs one at a time until the batter looks light and lemony.

Add the vanilla, mashed bananas, and buttermilk. Blend for 30 seconds to combine.

Slowly add the dry mixture and mix until mostly blended. Do not overmix.

Fold in the chopped nuts by hand.

Pour the batter into the prepared pan and tap the pan on the counter to release large air bubbles.

Bake for about 1 hour and 15 minutes, or until the loaf is golden and a toothpick inserted in the center comes out clean. Tent with foil if the top browns too quickly.

Let the loaf sit for 5 minutes in the pan, then invert onto a wire rack to cool completely before slicing.