Buttermilk Banana Bread

Preheat the oven to 350°F. Spray a 9×5 loaf pan with nonstick spray. Line the bottom and up the short sides with a strip of parchment paper. Spray again with nonstick spray. Set aside.
In a medium bowl mash 2 of the bananas with a fork, leaving them slightly lumpy. Slice the remaining banana thinly, and set aside.
In a large bowl stir together the butter and sugar. Mix in the eggs and vanilla and stir until smooth.
Add the buttermilk, mashed bananas, baking soda, and salt, and stir until blended.
Stir in the flour until just incorporated. Fold in the reserved sliced bananas, and walnuts.