Put 2 tablespoons of red wine vinegar into a large, non-stick frying pan and bring to a simmer. Then add 150ml of chicken stock and reduce the mixture by half over a high heat. Add 2 teaspoons of green peppercorns, crushing a few of them gently in the pan with the back of a spoon. Season and reduce then stir in 4 tablespoons of double cream. Simmer for one or two minutes until the sauce is slightly thickened.