Whisk together the flour, oats, brown sugar, cinnamon, and salt in a mixing bowl. Add in the cubes of cold butter and work them into the flour mixture with a pastry cutter or your hands. They should resemble small pea sized crumbles. Put the topping in the refrigerator while you make the apple filling.
Peel the apples and slice them thin, about 1/4-1/2 inch in thickness. You can also cut them into small 1 inch chunks if you prefer. Put the apples in a large mixing bowl with the maple syrup, vanilla, spices, salt, and cornstarch. Toss together until they're coated.
Pou the apple mixture into a 19x13 baking dish, 10 inch deep dish pie plate, or something similar in size. Distribute the crisp topping evenly over the apples. Bake on the middle rack of the oven at 350° F. for 45-50 minutes or until the top is golden brown and the apples are tender. Let it cool for 10 minutes before serving with vanilla ice cream.
Notes
Check the apple crisp at 30-35 minutes to see if the top is getting too brown. If it is, cover it loosely with a piece of aluminum foil.