Ballotine of Whiting and Mussels, Champagne Sauce

• 6 whole whiting, weighing 400 g each
• 1 kg mussels, thoroughly cleaned and scrubbed

Remove the heads and tails from the whiting and reserve. Bone the fish leaving the backs intact.

Soften the butter in a stockpot over a low flame, add the mirepoix and shallots and melt them in the butter for five minutes being careful not to colour them. Add the champagne, the heads, tails and bones of the whiting, the thyme and bay leaf and bring to the boil. Add the mussels, cover, r