Remove skin and bone and flake the fish into small pieces. Blend the butter and flour in a saucepan, and fry for a few minutes without browning. Add the milk and stir until boiling. Then put in the cod and the shrimps. Cook until thoroughly hot and season carefully. Make a deep border of mashed potatoes on a hot dish, pour the hash in the centre and sprinkle a little chopped parsley over the top.