Preheat oven to 350 degrees
Fill your muffin pan with muffin liners. Sit to the side.
In a small bowl combine brown sugar and cinnamon. Sit to the side.
Using a mixer, combine butter and sugar until completely combined.
Add eggs to the bowl and mix until everything is fully combined.
Slowly add in flour in 3 increments. (Add 1/3 of flour then mix. Repeat 2 more times)
Pour milk into bowl and mix until batter is creamy.
Mix diced apples into the brown sugar and cinnamon mixture.
Using a piping bag, add about 1tbs of batter to each muffin cup.
Add about a tbs of the apple mixture.
Top the muffin cups with more batter.
Top each muffin cup with about a tbs of the apple mixture and extra brown sugar and cinnamon.
Bake for 20-25 minutes or until each cupcake is done in the middle using a toothpick test.
Let muffins cool.
To make the glaze, just mix your powdered sugar and milk.
Drizzle desired amount on top of each muffin.