Preheat the oven to 350°F (175°C). Grease and flour a 9×5 inch loaf pan.
In a medium bowl, whisk together the flour, baking soda, salt, and 1 teaspoon ground cinnamon. Set aside.
In a large bowl, cream the softened butter and granulated sugar together until light and fluffy, about 3 minutes.
Add the eggs one at a time, beating well after each addition.
Mix in the vanilla extract.
Stir in the mashed bananas and sour cream until just combined.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.
Pour the batter into the prepared loaf pan and smooth the top with a spatula.
In a small bowl, combine the brown sugar and 1 teaspoon ground cinnamon. Sprinkle this cinnamon sugar mixture evenly over the top of the batter.
Bake for 55-60 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.