Make the apple filling, adding a tiny bit more lemon juice so the apples don't brown. Store the apple filling in an air-tight container, in the fridge, for up to one day.
Then Make the crumble topping and put it in a separate ziplock bag, in the fridge. When ready to bake, remove from the fridge, and sprinkle the topping on top. Bake as directed.
To freeze apple crisp:
Prepare and bake the apple crisp as directed. Cool the crisp completely, then cover it with a double layer of aluminum foil. Freeze for up to 3 months. Thaw overnight in the refrigerator, then warm in a 350°F oven for 20-25 minutes or until heated through.Recipe adapted from Cooking Classy.