For the topping
Preheat your oven to 350°F (175°C) and grease a 9x5-inch loaf pan.
In a large bowl, combine the mashed bananas with the melted butter. Stir in the vanilla extract and the egg until well mixed.
Mix in the granulated sugar and brown sugar. Then, add the baking soda, salt, cream of tartar, and cinnamon, stirring until everything is combined.
Gently fold in the flour until just incorporated. Avoid overmixing to keep the bread tender.
In a small bowl, mix together the sugar and cinnamon for the topping.
Pour half of the banana bread batter into the prepared loaf pan. Sprinkle half of the cinnamon sugar mixture over the batter. Add the remaining batter on top and sprinkle the rest of the cinnamon sugar mixture evenly over the surface.
Bake for 55-65 minutes, or until a toothpick inserted into the center comes out clean.
Allow the bread to cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely.
