Wash the potatoes and cook in plenty of boiling water for 15-20 minutes. Then rinse with cold water, peel and leave to rest for a while. Brush the black salsifies vigorously, peel and place in vinegar water.
Halve the black salsifies and cook in boiling salted water for about 15 minutes. Peel and finely dice the onion. Melt the margarine. Sauté the onion in it, sauté the flour. Deglaze with stock and cream.
Bring to the boil while stirring constantly. Season to taste with salt, pepper and lemon juice. Cut the potatoes into slices. Fill potato slices, black salsify and ham into 4 small ramekins. Spread the sauce over them.
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 15 minutes. Serve garnished with parsley.