Preheat oven to 350 degrees F. Whisk together the 1/4 cup sugar and 1/2 teaspoon cinnamon. Thoroughly grease a 9×5 nonstick loaf pan with butter and the cinnamon-sugar mixture (swirl the pan around until it’s coated. Discard excess or use for something else. Watch the video, if you’re unsure.)
Mash 2 of the bananas to equal 1 cup. Slice the 3rd banana.
In a large bowl, whisk together the sugar and butter.
Whisk in the eggs and vanilla until combined.
Add in the flour, baking soda, and salt; stir together until just incorporated and smooth.
Stir in the mashed bananas and sour cream. Don’t over-mix.
With a rubber spatula, gently fold in the walnuts and chocolate chips.
Pour the batter into prepared loaf pan and spread evenly.
Arrange banana slices over the top and sprinkle with the turbinado sugar.
Place in oven and bake until a toothpick inserted in the center comes out clean, about 1 hour (start checking after 55 minutes.)
Cool in pan for 10 minutes, then transfer to a wire rack to cook completely.
