01 - Preheat the oven to 350°F.
02 - Pat duck legs dry with paper towels. Season all over with kosher salt, black pepper, and five-spice powder if using.
03 - Place duck legs skin side down in a cold, ovenproof skillet. Heat over medium for 8–10 minutes until the fat renders and the skin turns golden brown.
04 - Flip duck legs, transfer skillet to the oven, and roast for 1 hour. Baste with rendered fat halfway through cooking. The duck is ready when the skin is crisp and the meat tender.
05 - Meanwhile, combine plums, honey, brown sugar, red wine vinegar, soy sauce, shallot, garlic, ginger, red pepper flakes, and water in a saucepan. Bring to a simmer over medium heat.
06 - Simmer, stirring occasionally, for 20–25 minutes until plums are soft and sauce thickens. Mash or blend to desired consistency, then adjust seasoning to taste.
07 - Remove duck legs from the oven and let rest for 5 minutes.
08 - Plate duck legs with plum sauce and garnish with spring onions and fresh herbs if desired.