By Kit Chapman
Purée the fish in a food processor with the egg white and salt. Pass the purée through a fine sieve and put into a bowl over ice. Chill in the refrigerator for 1 hour.
Sweat the shallot in butter for 3 minutes. Add the mushrooms and sweat for a further 2 minutes. Add the white wine and reduce until dry. Cool.
Butter six savarin moulds,