Preheat the oven to gas 6, 200ºC, fan 180ºC. Season the chicken with plenty of salt and the black pepper. Heat the butter in an ovenproof frying pan and add the chicken breasts. Throw in the sage leaves and zest the lemon over the chicken. Cook over a medium heat. Squeeze in some lemon juice once the chicken breasts are browned, add a splash of water and place the pan in the oven. Roast for 15 minutes. Meanwhile make the potato salad. Wash and cut the potatoes into bite-sized pieces. Boil them in a pan of salted water until soft all the way through, adding the peas to cook for the last minute. Drain and allow to cool for 5 minutes. Toss in the mayo, add a drizzle of olive oil, and season. Remove the chicken from the oven and pour the pan juices into the potato salad and stir again. Serve up the warm potato salad with a carved chicken breast.
