Select firm white fleshed salted herrings with soft roes and soak them in milk to remove the salt. Fillet the fish, removing as many bones as possible, coat the inside surfaces of the fillets with a mixture of made English mustard and finely chopped onion then roll them up and tie with string.
Arrange in an earthenware dish with the roes. Boil sufficient vinegar with a Bouquet garni, onion, peppercorns and cloves to cover the fillets, then strain over the fish whilst boiling and allow to cool.
When cold, remove the fish, pass the roes through a fine sieve and mix this purée back into the vinegar with
Pour this mixture over the herrings and allow to marinate for 2–3 days. To serve, arrange the roll mops in raviers with a little of the marinade.