Preheat oven to 400F. Lightly grease a 9x9 inch baking pan and set aside.
Using a handheld electric mixer or a stand mixer fitted with the paddle attachment, combine 1 ½ cups flour, ½ cup butter, ¼ cup sugar, ⅛ teaspoon salt, 1 egg yolk and ½ teaspoon vanilla extract.
Beat on low speed until it resembles a coarse meal.
Press to the bottom of your pan using your hands. Make sure to really pack it in and get to all the corners.
Bake for 10-15 minutes or until it turns a light golden brown. Remove and let cool. Don't turn the oven off; lower the oven temperature to 350F.
While the crust is baking, melt 20 caramels in a heavy bottomed pan over low heat. When they are almost completely melted, add 2 tablespoons half and half and ¼ teaspoon salt. Stir to incorporate and remove from heat.
Next turn to your oat crumble: simply mix all ingredients together in a medium bowl.
Stir until combined and evenly moist.
To assemble your apple crumble bars, place chopped apples on top of baked crust.
Drizzle with caramel sauce.
Then top with oat crumble mixture.
Bake for 30-45 minutes or until the apples are tender and the crumble is crisp and golden brown.
Cool in the pan before cutting into squares. Drizzle with more caramel sauce and top with ice cream if desired.