4 ripe bananas, mashed
285g/10oz plain flour
1 tsp bicarbonate of soda
225g/8oz caster sugar
陆 tsp salt
1 tsp vanilla extract
110g/4oz butter, plus extra for greasing
85ml/3fl oz buttermilk (or normal milk mixed with 1陆 tsp lemon juice or vinegar)
2 free-range eggs