Preheat oven to 400 degrees and lightly oil a 9 by 9-inch glass or ceramic casserole dish. Shingle one layer of potatoes to cover the bottom of the casserole dish. Sprinkle over with some of the sliced onions, then layer with some of the sliced apples. Season with salt and pepper. Repeat the layering process until the entire product is used, making sure you finish with a layer of potatoes. When using a microwave, be sure to wrap the casserole in plastic and poke 2 holes in the plastic. Cook at high heat for 15 minutes. Remove the plastic and transfer to the preheated oven. Cook until well browned, approximately 10 minutes. Sprinkle with the grated cheese and bake until melted and lightly browned.
When using the oven, cover the casserole or wrap with aluminum foil bake 45 to 50 minutes. Remove the foil and bake until well browned. Sprinkle with the grated cheese and bake until melted and lightly browned.