1.Cut crusts from bread. Process prawns, onion. ginger. egg white, cornflour, soy sauce and pepper in a food processor until smooth.
2.Spread prawn mixture evenly onto one side of bread slices. Cut each slice into 4 triangles. Place sesame seeds on a plate. Press bread, prawn-side down, in sesame seeds to coat.
3.Heat oil in a wok or large heavy-based saucepan over moderately high heat (oil is ready when a cube of bread crisps quickly without absorbing oil). Deep-fry toast in batches, prawn-side down, 1 minute. Turn and cook for 30 seconds more, or until golden brown. Drain on paper towels. Serve.
Prawn mixture can keep in the freezer for up to three months.