Wash the potatoes and cook in boiling salted water for about 20 minutes. Then peel and possibly halve them. In the meantime peel and finely dice the onion. Wash and chop the herbs. Heat the fat and fry the onion until transparent. Sweat flour in it. Deglaze with stock and milk.
Simmer for about 10 minutes, stirring constantly. Season to taste with salt, pepper and nutmeg. Warm up the potatoes. Stir in half the herbs. Sprinkle with remaining herbs. Cut ham into thin slices. Add onion rings, cucumber slices and lemon to taste.