Preheat the oven to 400°F.
Peel and pit the apples. Slice into even sized slices, about 1/8 inches thick.
In a casserole dish or cast-iron skillet, add the sliced apples, sugar, vanilla, cornstarch, vanilla, cinnamon and lemon juice and mix until the apples are fully coated.
In a separate bowl, combine the flour, oats, brown sugar, cinnamon, pecans, and salt.
Add the cold cubed butter to the dry ingredients and with your hands or a dough blender mix in the butter to incorporate, mix until the mixture is crumbly. (Don’t overmix — you still want some chunks of butter. It should be crumbly, not smooth.)
Add the apple crisp topping over the apples, sprinkling evenly over all the fruit.
Bake at 400°F for 40-45 minutes, until the topping is golden brown and juices are bubbling around the edges. Remove it from the oven and cool it for 5-10 minutes.
Serve warm with vanilla ice cream, yogurt, or plain.