Preheat oven to 325°F (170°C). Lightly spray an 8½x4½-inch loaf pan with cooking spray. Line pan with parchment paper, letting excess extend over sides of pan.

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

In a large bowl, whisk together mashed banana, brown sugar, melted butter, sour cream, eggs, vanilla, and cinnamon. Fold in flour mixture just until combined. Spoon batter into prepared pan. Place Caramelized Banana, cut sides up, on top of batter.

Bake until a wooden pick inserted in center comes out clean, 1 hour and 15 minutes to 1 hour and 20 minutes. Let cool in pan for 10 minutes. Using excess parchment as handles, remove from pan, and let cool completely on a wire rack. Serve with softened butter.