Pre-heat the oven to 370F / 180C.
Cream together the butter and sugar until fluffy.
Add the eggs, one at a time, ensuring each is fully incorporated until continuing.
Stir in the vanilla extract.
Stir in the apple, banana and carrot.
In a separate bowl sieve together the flour, baking powder and salt.
Fold in half the flour mixture, followed by the milk, followed by the remaining flour mixture.
Use an ice cream scoop to divide mixture into a muffin pan lined with cases.
Bake in the oven for around 20 minutes, or until an inserted knife comes away clean.