Preheat the oven to 375°F (190°C).
In a large bowl, toss the sliced apples with the white sugar and cinnamon until evenly coated. Transfer the apple mixture to a 9-inch pie dish or baking dish.
In a separate bowl, combine the flour, oats, brown sugar, and salt. Cut in the cold cubed butter using a pastry cutter or two forks until the mixture resembles coarse crumbs.
Sprinkle the crumble topping evenly over the apple filling.
Bake for 40-45 minutes, or until the topping is golden brown and the apples are tender and bubbly.
Let the apple crumble cool for at least 15 minutes before serving. Serve warm, with a scoop of vanilla ice cream or a dollop of whipped cream, if desired.