1.Using a sharp knife, score skin on each duck breast in a 1.5cm diamond pattern.
2.Heat large frying pan to very hot. Place duck breasts, skin-side down, in pan; cook about 10 minutes or until skin is golden and crisp. Turn breasts over; cook 2 minutes then remove from pan. Stand duck breasts, covered, 10 minutes.
3.Meanwhile, cook apple in same cleaned pan, stirring, 2 minutes. Add sugar; cook, stirring, about 3 minutes or until apple is browned and tender.
4.Arrange endive, nuts and mint on serving plates. Slice duck breasts thinly then arrange on salad with apple; drizzle with combined vinegar and oil.
Sherry vinegar is a natural vinegar made from the sherry grape grown in the southwest of Spain; aged in oak, this traditional wine vinegar has a mellow sweet-sour taste, similar to balsamic, which makes it a perfect dressing for tender young greens, like the endive and mint used here.