You will need to make the butterscotch sauce before beginning the apple crisp bars.
Preheat oven to 350F. Grease a 9-13 baking dish with butter and then cut a piece of parchment paper to line the bottom and overhang the edges.
For the crust and topping: Add all the crust ingredients to a large bowl. With your fingers, mix and work the butter into the dry ingredients until thoroughly combined. Take out 2 1/2 cups of the mixture and reserve for the topping. Then take the remaining mixture and pour it into the prepared baking dish. Press down the crust to make an even layer. Bake for 10 minutes.
For the apple filling: While the crust is baking, peel and chop the apples. Then, in a large bowl, mix together all the filling ingredients. Once the crust comes out of the oven, spread the apple filling over it in an even layer and then sprinkle the reserved topping over it. Bake the crisp bars for 40-45 minutes, or until the topping is browned and the apples are soft.
Allow the crisp bars to cool completely in the baking dish. Once they are fully cooled, remove them by pulling them out with the parchment paper and transfer them to a cutting board. Cut them into bars and drizzle the bars with butterscotch sauce.