Duck is often paired with sweet fruit sauces (think duck a l'orange), which are designed to cut through the bird's richness. This recipe is an excellent variation on that theme, and matches a roasted whole duck with a sweet and tart red sauce made with mixed berries, honey, balsamic vinegar, and orange juice. Potatoes and chestnuts are roasted along with the duck, soaking up the flavorful juices while in the oven.