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

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

Mix the wet ingredients. Whisk in the granulated sugar, brown sugar, melted butter, oil, eggs, vanilla, and sour cream until well combined and glossy.

Combine the dry ingredients. In a separate bowl, whisk the flour, baking soda, salt, and cinnamon. This helps avoid clumps and ensures even rise.

Bring it together. Add the dry ingredients to the wet bowl. Stir gently with a spatula until just combined. Do not overmix. Fold in walnuts or chocolate chips if using.

Fill and bake. Pour the batter into the prepared pan and smooth the top. Bake for 55–65 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs but no wet batter. If the top is browning too quickly, tent with foil for the last 10–15 minutes.

Cool before icing. Let the loaf cool in the pan for 10 minutes, then lift it out and cool on a rack until just warm. This helps the icing set without melting off.

Make the icing. In a small bowl, whisk powdered sugar, 2 tablespoons milk or cream, vanilla, and a pinch of salt. Add more milk a teaspoon at a time until it’s thick but pourable—like heavy cream.

Glaze the loaf. Spoon the icing over the warm loaf and let it drip down the sides. Allow 15–20 minutes for the icing to set before slicing.

Slice and enjoy. Use a serrated knife to get clean slices, especially once the icing is firm.