Heat the butter in a wide saucepan, stir in the shallots until soft but not coloured. Deglaze with the wine and vermouth and reduce by half. Pour in the stock, return to the boil and reduce again by half. Add the cream and simmer until the sauce reaches the consistency of pouring cream. Using a sharp knife, slit each chicken breast horizontally three quarters of the way through and open up flat and season. Mix the sausage meat with the chopped herbs and spread over the chicken. Roll tightly in cling film and poach for 15-20 mins. Chill. Meanwhile reheat the veloute and stir in the mustard. Heat the oil and butter in a large frying pan. When is starts foaming, add the chicken rolls and fry – turning for about 5 mins until browned on all sides. Serve.