Preheat oven to 375 degrees F (190 degrees C). Grease 12 muffin cups or line with paper muffin liners.
In a medium bowl, stir together the flour, baking powder, baking soda, salt and cinnamon.
In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla. Beat in the flour mixture alternately with the milk; stir just enough to moisten the dry ingredients.
Fold in walnuts and apples.
Spoon batter into prepared muffin cups.
Bake for 20 minutes in preheated oven, or until done.