Peel and wash the potatoes and slice or slice them thinly. Heat 2 tablespoons of oil in a pan and fry the potato slices for 12-15 minutes while turning them until crispy. Season with salt and pepper.
Clean the mushrooms, wash them briefly if necessary and cut them in half. Peel and finely chop the onion. Wash thyme, shake dry and chop.
Remove the potatoes from the pan. Fry the mushrooms, onion and mustard seed in hot frying fat for approx. 3 minutes, turning. Add cream and thyme. Season with salt and pepper. Finely dice the mozzarella.
Preheat the grill of the oven (electric oven: 250 °C). Line a baking tray halfway with baking paper. Pat the steaks dry, cut the fat edge several times. Heat 1 tablespoon of oil in a pan. Fry the steaks for 2-3 minutes on each side.
Season with salt and pepper.
Put the steaks on the tray. Spread potato slices and mushroom cream on top. Sprinkle with mozzarella and then grill under the hot grill for 3-4 minutes.