Prep the pan and oven: Heat the oven to 350°F (175°C). Line a 9x5-inch loaf pan with parchment, leaving overhang for easy lifting. Lightly grease the sides.

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

Whisk the wet ingredients: Add melted butter, oil, brown sugar, granulated sugar, eggs, vanilla, and yogurt or sour cream. Whisk until smooth and glossy.

Combine dry ingredients: In a separate bowl, whisk flour, baking soda, baking powder, salt, and cinnamon (if using).

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

Fill and bake: Pour batter into the prepared pan and smooth the top. Bake for 55–65 minutes, or until a toothpick comes out mostly clean with a few moist crumbs. If the top browns too fast, tent loosely with foil at the 45-minute mark.

Cool completely: Let the loaf cool in the pan for 15 minutes. Lift out using the parchment and transfer to a rack. Cool fully before frosting.

Make the frosting: Beat softened cream cheese and butter together until smooth and fluffy, 2–3 minutes. Add powdered sugar 1/2 cup at a time, beating well. Mix in vanilla and a pinch of salt. Add a teaspoon of milk or cream if you want a silkier spread.

Frost and finish: Spread a thick, even layer over the cooled loaf. For a bakery look, make soft swoops with an offset spatula. Chill for 20 minutes to set before slicing.

Slice and serve: Use a sharp knife, wiping between cuts for clean slices. Enjoy slightly chilled or at room temperature.