Preheat oven to 350°.
Cream the butter and sugar together until well combined.
Add in the egg and mix thoroughly.
Add the flour, baking powder and salt. At this point, the ‘batter’ should resemble a packaged muffin mix. It will be very very dry.
Slowly add in the milk and mix until the batter is smooth.
Fold in the diced apples.
Sprinkle the cinnamon and sugar* on top of the batter and fold 3 times. You'll want cinnamon and sugar throughout the batter, not completely mixed in.
Using a cookie scoop, scoop the batter into muffin tins.
Bake at 350°. For the mini muffins, bake for 15 minutes. For the regular muffins bake for 17-20 minutes or until a toothpick comes out clean.
While the muffins are baking, combine all vanilla glaze ingredients together and set aside.
When the muffins are finished baking, take them out of the oven and let them set for a few minutes.
When they are cool enough to handle but still warm, dip the tops of the muffins into the vanilla glaze.
Let cool on a wire rack or just dig right in like I usually do. :)