Wash the potatoes and boil them with their skins in boiling water for about 20 minutes. Then drain, rinse and peel. Let it cool down a little.
Preheat oven (electric cooker: 220 °C/circulating air: 200 °C/gas: see manufacturer). Pat steaks dry. Remove fat layer and tendons. Cut each steak crosswise 4-6 times. Cut sheep's cheese into pieces and stick into the incisions (see
Tip). Season steaks with salt and coarse pepper. Place in an ovenproof dish. Turn down the oven temperature (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Cook steaks in a hot oven for 12-15 minutes.
If necessary, switch on the grill of the oven for 2-3 minutes at the end. Take out, cover the mould with aluminium foil and let the steaks rest for about 10 minutes.
Cut the cooked potatoes into cubes (approx. 2 x 2 cm). Melt butter in a pan. Fry the potato cubes all around for about 10 minutes until golden brown. Season with salt and pepper. Wash parsley, shake dry and chop.
Add the parsley to the potatoes and flip through. Keep potatoes warm.
In the meantime peel and finely dice the onion. Clean the mushrooms, wash them briefly if necessary and dab them dry. Heat the oil in a large pan. Fry the mushrooms for about 5 minutes while turning them. Fry the onion briefly.
Stir in cream and crème fraiche. Bring to the boil and simmer for 3-4 minutes. Season with salt and pepper. Wash the thyme, shake dry and remove the leaves. Add the thyme to the mushrooms. Serve everything.