700 gmgreen school prawns, peeled16thin slices of white bread½cos lettuce, coarsely shredded2 tspWorcestershire sauceMayonnaise2egg yolks1 tspEnglish mustard powder1 tbspwhite wine vinegar200 mllight olive oil
For mayonnaise, using a food processor, pulse egg yolks, mustard and vinegar until combined. With motor running, add olive oil in a thin stream until emulsified and thick. Season to taste with sea salt and freshly ground white pepper. Makes 1 cup.
Cook prawns in boiling, salted water until just pink (3-4 minutes). Remove and cool.
Spread one side of each bread slice with mayonnaise. Top half the slices with half the lettuce, leaving a 2½ cm border. Top with prawns, a few drops of Worcestershire sauce, season to taste, then top with remaining lettuce and bread slices. Press firmly on the edges to seal the sandwiches. Trim crusts, cut in half and serve immediately.