Preheat oven to 350 degrees F. Grease a 15x10x1-inch baking pan; set aside.
In a large bowl, combine cake mix, brown sugar, melted butter, and eggs. Beat with an electric mixer on medium speed for about 1 minute or until combined, scraping bowl occasionally.
Pat dough into prepared pan. Sprinkle with butterscotch chips. Bake in the preheated oven for 15 to 20 minutes or until a toothpick inserted in center comes out clean. Cool completely in pan on a wire rack until room temperature. Cut into bars. Makes approximately 32 bars.
For the apples:
Add butter to pan over medium low heat and melt. Next stir in brown sugar and cinnamon then add in apples. Allow the apples to cook in the sauce until they become tender and sauce develops (about 7-12 minutes). Set aside.
For the Butterscotch Sauce:
Add butterscotch chips to microwave safe bowl then pour milk.
Microwave at 20 second intervals and whisk after each session until combined. It usually takes about 1 minute. If sauce is too thin, add more chips, if too thick, add a bit more milk and whisk until smooth.
Spoon apples over each of the bars along with butterscotch sauce and serve.
You can also replace the butterscotch with caramel sauce.