Prep the pan and oven: Preheat your 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 cups.
Whisk wet ingredients: Add the melted butter, oil, granulated sugar, brown sugar, eggs, yogurt or sour cream, and vanilla.
Whisk until well combined and glossy.
Combine dry ingredients: In a separate bowl, whisk the flour, baking soda, salt, and cinnamon. This helps distribute the leavening evenly.
Bring it together: Add the dry mixture to the wet mixture. Stir gently with a spatula until just combined.
A few streaks of flour are okay—don’t overmix.
Fold in extras: If using nuts or chocolate chips, fold them in now. Keep the stirring light.
Fill the pan: Scrape the batter into the loaf pan and smooth the top. For a pretty split, run a buttered knife down the center.
Bake: Bake for 55–70 minutes, depending on your oven.
The top should be deep golden and a tester inserted in the center should come out with a few moist crumbs, not wet batter.
Cool properly: Let the loaf cool in the pan for 10–15 minutes, then lift it out to a wire rack. Cool at least 45 minutes before slicing to keep it from crumbling.
Slice and enjoy: Use a serrated knife for clean slices. Serve warm or at room temperature.