Preheat the oven to 350°F. Be sure to adjust the oven rack to the lower-middle position.
Grease the pan: Grease a 8.5 x 4.5 inch light colored loaf pan with softened butter. Evenly spread a thin layer of butter over the interior surface of the loaf pan. Be sure to cover the bottom and sides, including the corners. Add a tablespoon or two of all-purpose flour to the pan. Tilt and rotate the pan, tapping it gently, to distribute the flour evenly across the greased surface. The flour will stick to the butter, creating a light, floury coating. Hold the greased and floured pan upside down over the sink or a trash can to allow any excess flour to fall out. Gently tap the pan to help remove loose flour.
Melt the butter in a microwave safe bowl in 30 second intervals until fully melted. Be sure to cover it so it doesn't splatter. Set melted butter aside to cool for ~10 minutes. Then add in the sugar.
1/2 cup unsalted butter, melted and cooled for ~10 minutes, 1 cup granulated sugar
Whisk the melted butter and sugar together in a medium sized mixing bowl for 1-2 minutes. It should look like a paste.
Add in the eggs, 1 at a time, whisk until mixed.
2 large eggs, room temperature
Then add in the mashed bananas, sour cream, and vanilla extract.
1 1/4 cup mashed ripe/over ripe bananas, 1/4 Heaping cup sour cream, room temperature, 2 tsp. vanilla extract
Sift in the dry ingredients and mix with a rubber spatula just until combined. Do not over mix.
2 cups all purpose flour, spooned and leveled, 1 tsp. baking soda, 1 tsp. kosher salt, 1/2 tsp. ground cinnamon
Pour into the prepared pan, smoothing out the top. Bake 60-65 minutes or until a toothpick inserted into the middle comes out clean. The batter will appear set and the tops will be golden brown.
Cool in pan on a wire rack for ~30 minutes. Release/tap bread out of pan. Cool completely before slicing. Slice and enjoy! (I love popping a slice in the microwave for 10-15 seconds then topping with butter!)