Preheat and prep: Heat your oven to 350°F (175°C). Grease and line an 8x8-inch square pan or a 9-inch round pan with parchment.
Mash the bananas: In a large bowl, mash the bananas until mostly smooth with a few small lumps. You should have about 1 1/4 to 1 1/2 cups.
Whisk the wet ingredients: Add granulated sugar, brown sugar, oil, eggs, yogurt (or sour cream), and vanilla to the mashed bananas.
Whisk until well combined and glossy.
Combine the dry ingredients: In a separate bowl, whisk flour, baking soda, baking powder, salt, and cinnamon.
Bring it together: Sprinkle the dry mix over the wet mixture. Gently fold with a spatula until just combined. Do not overmix; a few small streaks of flour are fine.
Pan and level: Pour the batter into the prepared pan and smooth the top. Tap the pan lightly to release air bubbles.
Bake: Bake for 30–38 minutes, depending on your pan and oven.
The cake is done when the top is golden and a toothpick comes out with a few moist crumbs, not wet batter.
Cool: Let the cake cool in the pan for 10 minutes, then lift it out and cool completely on a rack if you plan to frost. For serving plain, you can slice while slightly warm.
Make the frosting (optional): Beat cream cheese and butter until smooth. Add vanilla and salt.
Gradually beat in powdered sugar until creamy and spreadable.
Frost and serve: Spread a generous layer of frosting over the cooled cake. Slice into squares and enjoy.