Peel and wash the potatoes and cut into small cubes. Cover and cook in plenty of salted water for about 15 minutes. After about 5 minutes add noodles and cook.
Grate cheese. Bring cream and milk to the boil. Melt 2/3 cheese in it while stirring. Season sauce with salt, pepper and nutmeg. Drain potatoes and noodles.
Grease a large oven dish. Mix potatoes, noodles and sauce. Sprinkle with remaining cheese. Bake in a hot oven (electric cooker: 200°C/circulating air: 175°C/gas: level 3) for about 5 minutes until the cheese has melted.
Peel onions and cut them into rings. Fry in hot butter until golden brown. Serve with onion rings. Sprinkle with parsley.