Skin a three and one-half pound haddock, and cut in fillets. Arrange in buttered baking-pan, pour around fish three tablespoons melted butter, three-fourths cup white wine to which has been added one-half tablespoon lemon juice, and two slices onion. Cover and bake. Melt two tablespoons butter, add two tablespoons flour, and pour on liquor drained from fish; then add one-half cup Fish Stock (made from head, tail, and bones of fish), two tablespoons heavy cream, yolks two eggs, salt, and pepper. Remove fillets to serving dish, pour over sauce strained through cheesecloth, and sprinkle with finely chopped parsley.