To prepare a sweet potato apple and onion gratin cheese recipe, you'll first need to prepare the sweet potatoes. Peel and slice the apples and cut them into quarters. Place the quartered apples in the bottom of an 8x8-inch baking dish. Add the shredded cheddar cheese, sour cream, and salt and pepper to taste. Pour the mixture into the dish and bake for 30 minutes at 325 degrees F or until the cheese is melted and bubbly. Remove from the oven and sprinkle with the chopped parsley. Serve warm or at room temperature.