Grease a 9×5-inch loaf pan with a bit of butter and dust with flour, set aside. Preheat your oven at 180 C, gas mark 4.
mix together flour, baking soda, salt, and cinnamon in a large bowl.
beat the butter and brown sugar together on high speed until smooth and creamy. It takes a couple of minutes. Switch down to medium speed, and add the eggs one by one, beat well after each addition and finally beat in the yogurt, mashed bananas and vanilla extract.
You can now fold in the dry mix of flour gently, until no flour pockets remain.
Lastly fold in the nuts or raisins if using.
Bake for 60 minutes, once toothpick inserted should come out clean!