Reduction
Bring the stock to the boil along with all the other ingredients up to and including the bay leaf, turn down the heat. Reduce the liquid to approx. 2 tbsp, strain and return to the pan.
Sauce
Add the full-fat cream and single cream, bring to the boil, turn down the heat, reduce over a low heat for approx. 2 mins., stirring occasionally until the sauce is thick and creamy, season.