Preheat your oven to 300°F (150°C) and line a 9×9-inch pan with parchment paper.

Prepare the crust: In a medium bowl, mix together the melted butter, light brown sugar, salt, and vanilla extract. Gradually stir in the flour until combined. Spread the mixture evenly into the prepared pan.

Bake the crust for 15 minutes, then take it out of the oven.

Make the apple filling: In a large bowl, toss the sliced apples with vanilla extract, cinnamon, light brown sugar, and flour until all slices are coated.

Create the crumble topping: In another bowl, blend the melted butter, brown sugar, cinnamon, and salt. Add the flour and mix with a fork until the mixture becomes crumbly.

Layer the apple filling on the warm crust, pressing it down to ensure everything fits nicely. Sprinkle the crumble topping over the apples.

Bake for an additional 30-35 minutes or until the top is golden brown.

Allow the bars to cool at room temperature for 20-30 minutes before refrigerating for at least an hour, or preferably overnight.

Once set, cut into 9 bars and drizzle with caramel sauce before serving.