1. Preheat your oven to 350°F (175°C) and grease a 9×5 inch loaf pan.
2. In a bowl, whisk together the flour, baking soda, and salt. Set aside.
3. In a large mixing bowl, combine the melted butter and brown sugar, beating until smooth.
4. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
5. Mix in the mashed bananas and sour cream until fully incorporated.
6. Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Be careful not to overmix.
7. In a small bowl, combine the granulated sugar and cinnamon.
8. Pour half of the batter into the prepared loaf pan. Sprinkle half of the cinnamon-sugar mixture over the batter.
9. Pour the remaining batter into the pan and sprinkle the remaining cinnamon-sugar on top.
10. Use a knife to swirl the cinnamon-sugar into the batter gently.
11. Bake for 50-60 minutes or until a toothpick inserted into the center comes out clean.
12. Allow the bread to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.

I love involving my kids in this step—letting them sprinkle and swirl the cinnamon-sugar is messy, yes, but a whole lot of fun!