Prep the pan and oven: Heat the oven to 350°F (175°C). Grease a 9x5-inch loaf pan and line it with a parchment sling for easy removal.

Mash the bananas: In a large bowl, mash the bananas until mostly smooth with a few small lumps. You should have about 1 1/3 to 1 1/2 cups.

Whisk the wet ingredients: Add the sugars, melted butter, oil, eggs, sour cream, and vanilla. Whisk until well combined and glossy.

Combine the dry ingredients: In a separate bowl, whisk the flour, baking soda, baking powder, salt, and cinnamon.

Bring it together: Add the dry ingredients to the wet. Stir with a spatula just until you no longer see dry flour. Do not overmix.

Add mix-ins: Fold in nuts or chocolate chips if using. Keep the batter thick and cohesive.

Fill the pan: Scrape the batter into the prepared pan and smooth the top. For a pretty finish, sprinkle a little sugar over the surface.

Bake: Bake for 55–70 minutes, until the top is deep golden and a toothpick inserted in the center comes out mostly clean with a few moist crumbs. If the top browns too fast, tent loosely with foil for the last 15 minutes.

Cool properly: Let the loaf cool in the pan for 10–15 minutes, then lift it out and cool on a wire rack for at least 1 hour before slicing.

Slice and enjoy: Use a serrated knife for clean slices. Serve warm or at room temperature.