Wash the potatoes thoroughly. Cook in boiling water for about 30 minutes. Clean and wash spring onions. Cut off the green of the spring onions and cut into fine rings, chill.
Cut the white of the onion into rings. Heat the oil in a pot and sauté the onion. Add the tomatoes and chop them in the pot with a wooden spoon. Add 125 ml water, bring to the boil and stir in the stock.
Season with salt, pepper and sugar. Let simmer at mild heat for about 30 minutes. Drain the potatoes and let them evaporate. Spread 4 square pieces of aluminium foil (approx. 28 x 28 cm) with oil.
Sprinkle with herbs. Cut the potatoes in the middle once lengthwise and wrap them in the foil. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 25-30 minutes.
Drain the olives. Sheep's cheese crumbles. Season the sauce again. Wrap potatoes out of the foil, press them apart so that they break open at the cuts. Pour sauce into the potatoes, add remaining sauce extra.
Sprinkle with spring onions, olives and cheese. Garnish with thyme.