Trim a large inch-and-a-half-thick porterhouse steak. Rub together a tablespoonful of butter and one of flour, add a pint of good strong stock, a tablespoonful of chopped onion, a bay leaf, a saltspoonful of celery seed, a level teaspoonful of salt and a saltspoonful of pepper. Bring to the boil and simmer gently for thirty minutes. Bake ten large mushrooms for ten minutes, add them to the sauce, and cover and stand it over hot water while you broil the steak quickly on each side until it is seared, then slowly for twenty minutes. Dish it on a hot platter, dust with salt and pepper. Add a tablespoonful of butter to the sauce, lift the mushrooms, place them over the top of the steak and pour the sauce over all.