Heat the oven to 200°C (180° fan) 400°F gas 6. Grease a 12 hole muffin tin.
Beat the butter and sugar in a mixing bowl until light and fluffy. Gradually beat in the eggs until blended.
Mash the bananas and beat into mixture until blended.
Gradually stir in the dry ingredients until incorporated. Fold in the raisins.
Spoon into the tins and bake for 20-25 minutes until golden. Cool in the tins for 5 minutes, then place on a wire rack to cool completely.