Vidalia^® Sweet Onions Au Gratin

5          cups cooked G&R Vidalia^® sweet onions (drained and chopped)
4½       cups grated cheddar cheese
½         cup self-rising flour
¼         teaspoon black pepper
½         teaspoon salt
6          tablespoons butter

Mix onions, 3½ cups cheese and remaining ingredients. Pour in two-quart casserole dish. Sprinkle 1 cup grated cheese on top. Bake in oven at 350 degrees for 30 minutes. Serves 10 to 12.