Partially cook egg noodles, drain and layer 1/2 on sm buttered casserole dish. Combine soup,milk and chipped onion,Chunk several slices of cheese into noodles, followed by 1/2 of the tuna. Pour a portion of the soup mixture on top of tuna-noodle layer, followed by parmesan cheese. Top with chunks of butter and remaining soup, followed by halved cheese slices. Bake at 350° for 20 min.