Preheat oven to 180°C. Line a loaf pan with baking paper
Mix the flour, baking soda, salt, and cinnamon together and set aside
Beat the butter and sugar until smooth and creamy. Add the eggs one at a time, then in order the sour cream, mashed bananas, and vanilla extract until combined
Fold the dry ingredients into the wet ingredients, careful not to over mix. Fold in half of the nuts.
Pour batter into loaf pan and bake for 40-60 minutes, cover top if needed to prevent too much browning.
Allow to cool in the pan for 1 hour, remove and slice.