Preheat and prep: Heat the oven to 350°F (175°C). Grease a 9x5-inch loaf pan and line it with a parchment sling for easy removal.

Mix the cinnamon sugar topping: In a small bowl, combine the sugar and cinnamon. If using melted butter, set it aside separately for brushing later.

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, and vanilla to the bananas. Whisk until the mixture looks glossy and well combined.

Add the dairy: Stir in the sour cream or yogurt until the batter is silky and uniform.

Combine the dry ingredients: In a separate bowl, whisk the flour, baking soda, baking powder, salt, and cinnamon. This helps distribute the leavening and spice evenly.

Bring it together: Add the dry ingredients to the wet ingredients. Fold gently with a spatula until just combined. Do not overmix; a few streaks of flour are fine. If using nuts or chocolate chips, fold them in now.

Fill the pan: Spoon the batter into the prepared loaf pan and smooth the top. If using melted butter, lightly brush it over the surface.

Add the topping: Evenly sprinkle the cinnamon sugar mixture over the batter. Aim for full coverage so you get a consistent crust.

Bake: Bake for 55–65 minutes. The top should be deep golden and a toothpick inserted in the center should come out mostly clean with a few moist crumbs.

Cool properly: Let the bread cool in the pan for 10–15 minutes, then lift it out with the parchment and place on a wire rack. Cool at least 30 minutes before slicing to keep it tender and intact.

Serve: Enjoy warm, at room temperature, or lightly toasted with a small pat of butter. The cinnamon crust will stay crisp on day one and mellow slightly by day two.