In a bowl, beat together the butter and sugar until soft and fluffy. Crack in the egg, beat to combine, then stir in the milk.
Tip in the flour and fold into the mixture. Cut the fruit into chunks no bigger than 1cm, then stir into the mix.
Line a muffin tray with 12 small or 6 large muffin cases. Spoon the mixture into the muffin cases, then bake in the oven for 20 minutes or until risen and golden.