Prepare a court bouillon made with half water, half white wine, one onion and one carrot cut in slices, a bouquet of parsley thyme and bay leaf seasoning and cook it for a quarter of an hour. Melt some butter in a pan and toss lightly in it little button onions and sliced fresh mushrooms; remove them before they have reached the browning point. Cook in the court bouillon a pike, a carp or a biggish trout. When the fish is cooked remove it and put in in a fireproof dish with the little onions and slices of mushrooms. Let the court bouillon reduce a little more and make your sauce with this reduction, mixed with a white roux. Pour over the fish through a strainer and cook a little more; bind with a yolk of egg.