Wash potatoes thoroughly and cook in boiling salted water for 20-25 minutes. Then drain, rinse and peel. Cut the potatoes into slices. Wash, clean and slice the tomatoes. Sort the spinach, wash thoroughly and drain. Heat the oil. Sauté the spinach in it.
Add 1/8 litre of water, bring to the boil and stir in the stock. Season with salt and pepper. Divide the potatoes, tomatoes and spinach into four small gratin dishes or into a large dish. Grate cheese. Sprinkle cheese and sunflower seeds over the gratins. Bake in the preheated oven (electric cooker: 250 ° C/ gas: level 5) or under the hot grill for 5-7 minutes