Preheat oven to 350°F. Spray a 9×5 loaf pan with nonstick spray and line the bottom and up the short sides with a strip of parchment paper. Spray again with nonstick spray.

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 sour cream, mashed bananas, baking soda, and salt, and stir until blended.

Mix in the flour until incorporated.

Fold in the sliced banana, plus chocolate chips and walnuts if desired.

Pour batter into the prepared pan and bake for 50-60 minutes, or until a toothpick inserted in the center comes out clean.

Cool in the pan for 15 minutes, then lift the banana bread out of the pan using the parchment paper to cool on a wire rack.