Saucy Mixed Mushroom and Sweet Potato Casserole Recipe

Heat vegetable oil in skillet. Sauté onion and add mushrooms stirring frequently. Stir in thyme. Remove from heat and set aside. Combine half and half, salt and pepper in a large measuring cup, mix well. Layer the sweet potato and mushroom mixture in a large buttered casserole dish. Pour half and half mixture over the top. Bake covered at 350° for 20 minutes. Sprinkle cheese over the top and bake uncovered for 40 minutes longer.