PREP: Preheat the oven to 350 degrees. Line a 9x13-inch pan with parchment paper and set aside. Melt the 1 and 1/2 cups butter in the microwave and the set aside to cool back to room temperature.
CRUMBLE: In a large bowl, mix the melted and cooled butter (if the butter is still warm/hot it will make this crumble mixture greasy and prone to burning), brown sugar, flour, oats, baking soda, 1 and 1/2 teaspoons vanilla extract, and salt. Divide the mixture in half and press 1 half of it into the prepared 9x13-inch pan.
APPLES: Peel and core the apples, and then chop into small (~1/4th inch) pieces. Place the small pieces in a bowl and toss them with the lemon juice. Coat them in the flour and apple pie spice and sprinkle coated apples over top of the (unbaked) bottom crust.
CARAMELS: Place the unwrapped the caramels and the heavy cream in a medium-sized pot over medium-low heat. Heat and stir until completely smooth and then set aside to slightly cool and thicken. Do not heat above medium low; be patient while melting or the caramels will get hard. Once smooth and removed from the heat, stir in the 1/2 teaspoon vanilla extract and set aside. When slightly cooled, drizzle and gently spread caramel evenly on top of the apple layer.
TOP LAYER: Crumble and sprinkle the remaining crumble mixture on top of the caramel.
BAKE: Bake the bars in a 350 degree pre-heated oven for 25-30 minutes or until lightly browned around the edges and the top doesn't look wet or gooey. Remove from the oven and let stand at room temperature for at least an hour to set up. The bars are crumbly and hot straight out of the oven and they harden a bit with a gooey soft center after a few hours (Overall these bars are quite gooey/chewy).
STORAGE: Store bars in an airtight container at room temperature. These bars are best used by end of the second day. After that they begin to lose texture and flavor and become mushy. These bars don't freeze/thaw well.