Peel and devein the prawns, leaving the final segment of shell and tail attached. Combine remaining ingredients, except the olive oil and mustard, in large sauté pan. Bring marinade to a boil, reduce the beat and simmer for 5 minutes. Remove the pan from the heat and whisk in the olive oil and mustard. Add the prawns and simmer (do not boil) over low heat for 1½ minutes. Turn the prawns over and cook for another minute until just underdone. Remove the pan from the heat and let the prawns cool to room temperature in the marinade. (The prawns can be prepared ahead to this point and held, covered at room temperature, for an hour.)

When ready to serve, remove the prawns from the marinade and arrange on a serving plate. Put the extra marinade in a small bowl and serve with the prawns as a dipping sauce.

Makes 8 servings.