Bring the wine to the boil along with all the other ingredients up to and including the peppercorns, reduce to approx. 100 ml, strain and return to the pan.
Bring the reduction to the boil while stirring. Reduce the heat, then remove the pan from the heat. Add the butter gradually while stirring with a whisk. Return the pan to the hob a few times to gently warm the sauce; it must not boil. Season the sauce.