In this moist apple crisp recipe, sliced apples, brown sugar, white sugar, oats, butter, cinnamon, and vanilla unite in this oat crumble layered crisp.
Preheat the oven to 350 degrees F (175 degrees C).
Combine flour, brown sugar, oats, melted butter, and cinnamon in a bowl; stir until crumbly. Press ½ oat mixture into a 9x13-inch baking dish; cover with sliced apples.
Combine white sugar, water, cornstarch, and vanilla extract in a medium saucepan over medium heat; cook and stir until thick and clear, about 10 minutes. Pour over sliced apples; top with remaining ½ oat mixture.
Bake in the preheated oven until bubbly and golden, about 45 minutes.