Preheat the oven to 350°F (175°C). Grease a 9×5-inch loaf pan and set aside.
In a medium bowl, whisk together the all-purpose flour, baking soda, salt, and 1 teaspoon ground cinnamon until well combined.
In a large bowl, cream the softened butter and granulated sugar together until light and fluffy using an electric mixer.
Add the eggs one at a time to the butter mixture, beating well after each addition.
Mix in the vanilla extract.
Stir in the mashed bananas and sour cream until combined.
Gradually add the dry ingredients to the wet ingredients, mixing just until combined. Do not overmix.
Pour the batter into the prepared loaf pan and spread evenly.
In a small bowl, combine the brown sugar and 1 teaspoon ground cinnamon for the topping.
Sprinkle the cinnamon-sugar mixture evenly over the top of the batter.
Bake for 55 to 60 minutes, or until a toothpick inserted into the center comes out clean.
Remove the bread from the oven and allow it to cool in the pan for 10 minutes.
Transfer the bread to a wire rack to cool completely before slicing.