Preheat the oven to 350°F (175°C) and line an 8x8-inch baking pan with parchment paper, leaving an overhang on the sides.

In a large bowl, whisk together flour, granulated sugar, and salt. Use a pastry cutter to incorporate cold butter until the mixture forms pea-sized crumbs.

Transfer half of the crumb mixture to the prepared pan and press firmly into an even layer to create the base crust.

Bake the crust for 15 minutes or until lightly set.

In a separate bowl, toss the diced apples with lemon juice, brown sugar, cinnamon, and nutmeg until evenly coated.

Spread the apple mixture in an even layer over the par-baked crust.

Incorporate the rolled oats into the remaining crumb mixture and sprinkle evenly over the apple layer.

Bake for 30 to 35 minutes until the topping is golden brown and the apple filling is bubbling.

Remove from the oven and immediately drizzle the caramel sauce over the surface, then sprinkle with coarse sea salt.

Cool completely in the pan at room temperature before refrigerating for at least 2 hours to set before slicing into 16 bars.