Place all the ingredients in a food processor or liquidizer and process until smooth. Spoon into a serving dish and chill until required.
to make the fish tempura
Skin the fish and cut into 1cm/½2 thick strips, season with salt and pepper.
Place the flour in a bowl and make a well in the centre. Drop in the egg and add half of the soda water, beat until smooth. Next gradually beat in the remaining water to produce a thin smooth batter.
Heat the oil in a wok or deep fat fryer to 180℃.
Dip the fish into the batter and deep fry in batches for 2 minutes until crisp and golden.