Apple Crunch a la Mode

Preheat an oven to 350 degrees F (175 degrees C). Grease a 9x13 inch baking dish.

Scatter sliced apples in the prepared baking dish. Whisk together the white sugar, cold water, cornstarch, and vanilla extract in a small saucepan. Cook over medium heat until syrup is clear, and all sugar had dissolved, about 5 minutes. Pour hot syrup over the fruit.

Stir together the flour, brown sugar, oats, melted butter, walnuts, and cinnamon until crumbly. Scatter crumble over fruit mixture.

Bake in preheated oven until the top is brown and the crunch is bubbly, about 1 hour.