Spanish Fricasseed Shrimps

Heat 2 tablespoonfuls of butter; add 1 onion chopped and 2 cups of
tomatoes. Let fry; then stir in 1 tablespoonful of flour; add 1/2 cup
of water; let boil; add 1 quart of shrimps, salt, pepper and parsley.
Let all cook twenty minutes. Stir in the yolk of an egg. Remove from
the fire. Put some boiled rice on a platter; add the shrimps and pour
over the sauce. Serve very hot.