Preheat the oven to 350°F (175°C) and lightly grease a 9-inch baking dish.
Combine the sliced apples with lemon juice, brown sugar, granulated sugar, cinnamon, nutmeg, cornstarch, vanilla, and salt until evenly coated. Transfer the mixture to the prepared baking dish.
In another bowl, mix the flour, oats, brown sugar, granulated sugar, cinnamon, and salt. Cut in the cold butter until coarse, crumbly clusters form.
Sprinkle the crumble topping evenly over the apples, covering the fruit completely without pressing it down.
Bake for 40 to 45 minutes, or until the topping is golden brown and the apple filling is bubbling around the edges.
Scoop warm apple crumble into bowls and top each serving with a generous scoop of vanilla ice cream. Drizzle with caramel sauce if desired.