Cream butter and sugar until light and creamy. Stir in the mashed bananas and beat to combine thoroughly. Beat in the eggs, one at a time, blending well. Sift flour and salt onto mixture and stir well.
Dissolve bicarbonate of soda in water and stir into mixture. Add baking powder and stir well.
Pour batter into muffin moulds and bake for 20 – 25 minutes.
Cool in tin, then turn out onto a wire rack to cool completely.