Preheat the oven to 180 ° C (convection). Clean and halve the mushrooms. Peel the onions and cut into fine strips.
Heat the oil in a pan and sear the steaks all over. Salt, pepper, remove from the pan. Place on a baking sheet and cook in the preheated oven for 9 minutes.
Melt the butter in the pan and stir-fry the mushrooms, onions and rosemary sprigs for 4 minutes. Salt, pepper and pour in the cream and bring to the boil briefly.
Toast the toast in the toaster, place on 2 plates, place the steaks on top and serve with the mushroom and onion sauce. Citrus salad tastes good with it.