1) Place 4 knobs of butter in a pot on a hot flame and add in the shallots. Stir quickly with a tablespoon for one minute. Add the wine, bay leaf, a sprig of thyme, three ladles of fish stock and bring it to the boil and let it reduce by half.
2) Now add the cream, bring it up to the boil, and reduce it by 1/3.
3) When it is reduced, grab a clean saucepan and sieve and pour the stock through to the other saucepan through the sieve and a nice white sauce remains.
4) Add a pinch of salt and pepper and some chopped parsley, bring it back up to the boil and keep whisking it. Add two knobs of butter and keep swirling the sieve around as the sauce becomes thicker. The sauce is ready to serve.