Peel, wash and roughly dice the potatoes. Cover and precook in salted water for about 10 minutes. Drain and let drain. Clean the mushrooms, wash them briefly if necessary and cut them in half depending on size. Clean, wash and chop the spring onions.
Heat 1 tablespoon of clarified butter in a large frying pan. Fry the potatoes for about 10 minutes while turning them over. Season with salt and pepper, remove and keep warm.
Heat 1 tbsp. clarified butter in the frying fat. Fry the mushrooms for about 5 minutes. Fry spring onions and oregano for about 2 minutes. Season with salt and pepper. Dust with flour and sweat on. Deglaze with cream and 1⁄8 l water.
Bring to the boil and simmer for about 5 minutes. Stir in mustard, season sauce with salt and pepper. Fold in potatoes. Sprinkle the potato and mushroom pan with fresh oregano leaves as desired.