Beat the steaks and roll them in flour. Fry them until almost done in a preheated greased pan. When the steaks are almost done, remove them from the pan and in it fry the mushrooms until soft (if necessary add more oil).
Cut the onion into crescents. When the mushrooms are ready, arrange everything in a fireproof casserole, by laying onions, steak and mushrooms on top. Top up with the water to gently to cover the steaks and bake in the oven for 40-50 minutes.
If it is a strong oven, add water, but not much. Bake until tender and a little water must remain for the sauce.