Preheat oven to 350°F

In medium bowl, combine flour, oats, brown sugar, cinnamon and melted butter. Stir until crumbly. Press half the oats mixture into a 9x13 inch baking dish. Cover with sliced apples.

In a medium sauce pan, combine white sugar, cornstarch, water and vanilla. Cook, stirring, until thick and clear, 10 minutes. Pour over apples. Cover apples with remaining crumble mixture.

Bake in preheated oven 45 minutes, until bubbly and golden.