Making Mousseline

A mousseline consists of puréed raw fish, bound with egg whites and enriched with cream. The balance of ingredients is delicate: not enough fish means the mousseline will be tasteless; too much makes it heavy. Too much egg white gives a solid consistency; too little—or too much cream—makes the mousseline fall apart during cooking. Standard proportions are ½ lb/250 g raw fish to 1