SPANISH MACKEREL À LA CASTILLANE

Open a Spanish mackerel, take out most of the backbone, season with salt and pepper, and stuff with seasoned crumbs. Put into a buttered baking-dish with two sliced onions, a bunch of parsley, half a cupful of Sherry, and two cupfuls of white stock. Cover with a buttered paper and cook for half an hour in the oven, basting as needed. Take up the fish, strain the sauce and thicken with butter and flour cooked together. Season with lemon-juice and anchovy paste, add a tablespoonful of butter, pour over the fish, and serve.