Preheat the oven to 350°F. Spray a 9x5 loaf pan with baking spray, set aside.
Cream together the butter and brown sugar in the body of a stand mixer with the paddle attachment or in a large bowl with an electric hand mixer until light and fluffy, 2 minutes.
Add the eggs one at a time, stirring them in completely after each addition. Scrape down the sides.
Add the mashed bananas, sour cream, cinnamon, and vanilla, mix it in until combined fully. Scrape down the sides.
Lastly, add the flour, baking soda, baking powder, and sea salt into the mixer. Stir together until just combined with no dry patches.
Pour the batter into the loaf pan and smooth out the top.
Bake for 55-65 minutes until a toothpick inserted into the center comes out clean. At the 20 minute mark, very loosely place a piece of foil on top so the bread doesn’t get too brown.
Place the pan on a wire rack and let it cool for 10 minutes. Take the bread out of the pan and let it cool completely on the wire rack. Serve warm or room temperature.