Cover the potatoes and boil them in water for about 20 minutes. Drain, rinse with cold water and peel.
For the sauce, heat butter in a pot. Stir in flour and briefly sauté lightly. Deglaze with milk and bring to the boil while stirring. Stir in stock and simmer for about 5 minutes. Grate cheese. Melt half the cheese in the sauce.
Season to taste with salt and pepper. Wash parsley and shake dry. Pluck off leaves, chop them and stir into the sauce.
Preheat oven (electric cooker: 200°C/ circulating air: 175°C/ gas: level 3). Peel and wash carrots and Mairübchen. Cut carrots into slices and Mairübchen into cubes. Cut potatoes into pieces.
Put the potatoes, carrots and turnips in an ovenproof dish. Pour sauce over it and sprinkle with the rest of the cheese and sunflower seeds. Bake in a hot oven for about 30 minutes.