Put the chicken breasts between pieces of cling film and flatten slightly by bashing with a pan. Unwrap and sprinkle on both sides with pepper
Heat the oil in a pan over a medium heat, then fry the chicken for 5 minutes, turning halfway through
Pour 2 tbsp balsamic vinegar over the chicken, add the juice of two Jaffa oranges, 150ml of chicken stock and sprinkle with the rosemary and salt. Bring to the boil, lower the heat and bubble gently for 5 minutes until tender, spooning with the sauce frequently and turning chicken halfway through
Stir in the sugar, butter, and rest of the vinegar, then sizzle for a few minutes until reduced and glossy
Put the chicken in a serving dish, spoon the sauce over and garnish with the remaining two oranges and rosemary
