To make the cupcakes:
Preheat oven as directed on the cake mix.
Line a 9-cup muffin tin with paper liners.
Prepare batter according to box directions.
Fill liners 2/3 full and bake according to box directions for cupcakes.
Allow to cool completely.
Use a knife to dice apples into smaller pieces.
Use a knife to core out a plug in the middle of each cupcake and fill with pie filling.
To make the frosting:
Whip the butter, brown sugar, cinnamon, and vanilla until fluffy.
Gradually add powdered sugar.
Add milk until you reach the desired consistency.
Transfer to a piping bag and frost each cupcake.