Prep the pan and oven: Heat the oven to 350°F (175°C). Grease a 9x13-inch baking pan and line with parchment, leaving a bit of overhang for easy lifting.

Mash the bananas: In a large bowl, mash 3 large ripe bananas until mostly smooth with a few small lumps for texture.

Make the wet mixture: Whisk in melted butter, oil, granulated sugar, and brown sugar until glossy. Add eggs and vanilla; whisk until fully combined.

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

Bring it together: Add half the dry mixture to the banana bowl, stir gently, then add buttermilk. Stir in the remaining dry mixture just until no streaks of flour remain. Do not overmix.

Bake: Pour batter into the prepared pan. Bake 28–35 minutes, or until the top is golden and a toothpick in the center comes out clean or with a few moist crumbs.

Cool: Let the cake cool in the pan for 15 minutes, then lift out to a rack to cool completely before frosting.

Make the frosting: Beat softened cream cheese and butter until smooth and fluffy, 2–3 minutes. Add powdered sugar 1/2 cup at a time until you reach a spreadable consistency. Mix in a pinch of salt and lemon juice or vanilla.

Frost and finish: Spread frosting over the cooled cake. For a clean look, use an offset spatula. Add a light dusting of cinnamon or chopped toasted pecans if you like.

Slice and serve: Cut into squares. The cake tastes great at room temp or slightly chilled.