Peel and wash the potatoes and cut them into thin slices. Wash the fillet, dab dry with kitchen paper and cut into thin slices. Clean and wash the mushrooms. Clean and wash spring onions and cut them into rings.
Wash the thyme, shake dry and pluck the leaves from the stalks. Heat the oil in a large pan, fry the meat on each side, season with salt and pepper and remove from the pan.
Add the potatoes and mushrooms to the frying fat and fry for 8-10 minutes, turning all the way round, adding the spring onions and 3/4 of the thyme and frying briefly. Deglaze with stock, season with salt and pepper, bring to the boil and simmer covered for about 5 minutes.
Then add the meat, bring to the boil again, sprinkle with pink berries and remaining thyme and serve with crème fraîche.