Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan or line it with parchment paper.
In a large bowl, cream the butter and light brown sugar together until fluffy (about 3 minutes).
Add eggs, one at a time, beating well after each addition. Then stir in sour cream and vanilla extract until fully incorporated.
In a separate bowl, whisk together the flour, baking soda, and salt.
Slowly add the dry ingredients to the wet ingredients, stirring just until combined.
Fold in the mashed bananas until fully incorporated.
Pour the batter into the prepared loaf pan and spread evenly with a spatula.
Bake for 60-70 minutes, or until a toothpick inserted into the center comes out clean.
Cool the bread in the pan for 10 minutes, then transfer to a wire rack to cool completely.