Preheat the oven to 180°C (350°F).
Place the sliced apples in a baking dish and toss with granulated sugar, cinnamon, and vanilla.
In a bowl, rub the cold butter into the flour and salt using fingertips until the mixture resembles coarse breadcrumbs.
Stir in the brown sugar and rolled oats.
Sprinkle the crumble topping evenly over the apples.
Bake for 40 minutes, or until the topping is golden and the apples are bubbling.
Remove from the oven and allow to cool slightly before serving with ice cream, custard or cream.