In a bowl, combine 1/2 cup softened butter, 1 3/4 cups flour, 1/2 cup brown sugar and 1/4 tsp salt. Mix together with a pastry cutter or fork until well combined. (The mixture will appear dry.)
Spray a 10x10" baking pan with cooking spray.
Scrape mixture into baking pan and press down firmly and evenly to make the base.
Bake for 15 minutes, then remove from heat.
Filling
While the shortbread base is baking, peel apples and dice into small chunks.
Add apples to a mixing bowl and add in 1 tsp cinnamon, lemon juice, 2 tbsp flour and 2 tbsp sugar. Mix until apples are well coated.
Pour apple mixture over top of shortbread base and spread evenly.
Topping
Combine remaining ingredients (except for caramel) together in a mixing bowl and mix well.
Sprinkle the crumble mixture evenly over top of the apples.
Increase the oven temperature to 350 degrees F.
Bake for 40 minutes until the top of the apple crisp bars are golden brown.