1. To make the sauce, reduce the vermouth by half in a saucepan over high heat. Add the stock, boil, and reduce by half again. Add the cream and cook until thick. Set aside.

2. Meanwhile, preheat the oven to 475°F (240°C). Heat the oil in an ovenproof frying pan over high heat. Add the breasts skin-side down and cook about 4 minutes. Flip and season with salt and pepper. Transfer to the oven and roast about 10 minutes, until the juices run clear when pierced with a fork. Transfer to a platter.

3. Pour the fat from the skillet and return to medium heat. Add the sauce and stir to loosen the browned bits in the pan. Whisk in the mustard and chives. Slice the breasts and spoon the sauce on top. Serve hot.