Place the duck breast on a baking sheet skin side up. Prick the skin with a fork. Season with salt and pepper both sides. Bake for 12 minutes. Remove breast, tent with foil, and set aside to rest for 5 minutes.
In the meantime, place sugar, vinegar, and butter in a sauce pan. Reduce to a syrup over medium to medium low heat. Add beef stock and reduce substantially. Add port and reduce further.
Slice breast into thin slices, fan on plates, and nappe with sauce.
For candied peaches : 1. Preheat oven to 220°C.
Place butter and sugar in a small ovenproof sauce pan over medium heat. When butter and sugar are melted, add peaches, and place in oven.
Bake for about an hour until caramelized and soft. Stir every 10 minutes.
Let sit for 10 minutes or so before serving to cool slightly.