Prep the pan and oven. Heat 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 with a fork until mostly smooth with a few small lumps. You should have about 1 1/2 cups.

Whisk in the wet ingredients. Add melted butter, oil, granulated sugar, brown sugar, eggs, and vanilla. Whisk until well combined. Stir in the sour cream or yogurt.

Combine the dry ingredients. In a separate bowl, whisk together flour, baking soda, baking powder, salt, and cinnamon until evenly mixed.

Bring it together. Add the dry mixture to the wet mixture. Using a spatula, fold gently until just combined. Stop when you no longer see dry streaks. If using mix-ins, fold them in now.

Fill the pan. Scrape the batter into the prepared loaf pan and smooth the top. For a bakery-style split, run a buttered knife in a shallow line down the center.

Bake. Bake for 55–65 minutes. Check at 50 minutes and tent with foil if the top is browning too quickly. It’s done when a toothpick comes 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 and cool on a rack for at least 1 hour before slicing. This sets the crumb and keeps it from squishing.

Slice and enjoy. Serve plain, with butter, or toasted with a drizzle of honey.