Preheat oven to 350°F (175°C). Lightly butter a 10-inch cast iron skillet or 9x9-inch baking dish.

In a large bowl, toss the sliced apples with lemon juice, brown sugar, flour, cinnamon, nutmeg, and vanilla extract until every slice is evenly coated in spices. Layer evenly into the prepared skillet.

In a medium bowl, combine rolled oats, flour, brown sugar, chopped pecans, cinnamon, and sea salt.

Add the cold cubed butter. Use your fingertips or a pastry cutter to work the butter into the dry mix until coarse, pea-sized buttery crumbs and clusters form.

Scatter the buttery streusel evenly over the spiced apples, pressing down lightly so the topping clings together.

Bake at 350°F (175°C) for 35 to 40 minutes until the oat streusel turns deep golden-brown and the spiced apple juices are bubbling vigorously along the skillet edges. Let rest for 10 minutes to allow juices to thicken.

Scoop generous portions of warm crisp into shallow bowls. Crown with a large scoop of vanilla bean ice cream, drizzle liberally with warm salted caramel, and sprinkle with a pinch of flaky sea salt.