- Preheat the oven to 400 degrees F (200 degrees C). Lightly grease 12 muffin cups or line with paper muffin liners.
- Stir together flour, sugar, baking powder, cinnamon, and salt. Stir together milk, egg, and butter in a separate bowl. Stir egg mixture into flour mixture just until combined. Fold in chopped apples. Spoon batter into prepared muffin cups.
- Bake in the preheated oven until a toothpick inserted into center of muffins comes out clean, 20 minutes.