Poke holes in skin of legs at 45 degree angle with sharp knife. You want to go through skin but not through meat. Salt and pepper duck legs and leave for about an hour at least in the fridge
Put all the other ingredients in layers in a dutch oven. And then put duck legs on top, skin side down. Roast covered at 250f for 3 hours.
Carefully lay out legs and potatoes, onions and carrots on baking sheet, discard rosemary and sage, and save extra duck fat for other veggies. Broil for about 5-10 mins until crispy.
I made a Dijon cream sauce (Dijon, whole grain mustard and a bit of cream, warmed for a couple mins and finished with half Tbs of butter) to serve with the duck and blanched string beans tossed in duck fat. It would also be great with a sharp vinaigrette salad.