Cook the pasta and potato cubes together in salted water until al dente and drain. Bring the cream and the grated cheese to the boil until the cheese has melted. Then mix with the pasta and potatoes. Cut the onions into rings, half rings or cubes and let them turn golden brown in butter.
Arrange the pasta, potato and cheese sauce mixture on the plates and sprinkle with the roasted onions. Serve the applesauce separately in bowls.