Preheat the oven to 350°F (180°C). Butter a 9 x 5 inch (23 x 13cm) loaf pan and line with parchment.
In a large bowl, mix bananas, melted butter, sour cream, brown sugar, eggs and vanilla extract.
In a separate bowl, whisk flour, baking soda, cinnamon and salt.
Combine wet ingredients and dry ingredients until just combined
Pour into the loaf pan and bake for about 1 ½ hours, until a wooden skewer inserted into the center comes out clean.
Let cool in the pan for 10 minutes before inverting onto a wire rack to cool completely.
Store in an airtight container for up to three days. For longer storage, freeze in an airtight container for up to 2 months. Defrost at room temperature in the container for 2 hours.