Step 1: Preheat your oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish.
Step 2: In a large bowl, combine the sliced apples, lemon juice, granulated sugar, 1 teaspoon ground cinnamon, nutmeg, and a pinch of salt. Toss gently until the apples are evenly coated.
Step 3: Pour the seasoned apple mixture into the prepared baking dish, spreading it evenly across the bottom.
Step 4: Drizzle the warmed caramel sauce generously over the apples in the baking dish. Use a spoon to gently spread it if needed.
Step 5: In a separate medium bowl, combine the all-purpose flour, old-fashioned rolled oats, light brown sugar, 1/2 teaspoon ground cinnamon, and 1/4 teaspoon salt for the topping. Whisk them together.
Step 6: Add the cold, cubed unsalted butter to the dry topping ingredients. Using your fingertips or a pastry blender, work the butter into the mixture until it resembles coarse crumbs with some pea-sized pieces remaining.
Step 7: Evenly sprinkle the crumble topping over the caramel-drizzled apples in the baking dish. Do not press it down.
Step 8: Place the baking dish on a baking sheet (to catch any overflow) and bake for 45-55 minutes, or until the apples are tender when pierced with a knife, the filling is bubbly, and the crumble topping is golden brown and crisp. If the topping browns too quickly, loosely tent it with aluminum foil.
Step 9: Remove the crumble from the oven and let it cool for at least 15-20 minutes before serving. This allows the filling to set slightly.
Step 10: Serve warm with generous scoops of vanilla bean ice cream. Enjoy your classic caramel apple crumble a la mode recipe!