01 - Set the oven temperature to 300°F (150°C).
02 - Combine olive oil, melted butter, sage, garlic, lemon juice, lemon zest, salt, and pepper in a small bowl.
03 - Pat turkey legs dry and rub marinade thoroughly over each leg ensuring even coverage.
04 - Layer sliced onion, carrots, and celery in the bottom of a roasting pan; place turkey legs on top and pour broth around them, avoiding pouring over the meat.
05 - Cover pan tightly with foil and roast for 2 hours, basting turkey legs once halfway through with pan juices.
06 - Remove foil, increase oven temperature to 400°F (200°C), and roast uncovered for 15 minutes until skin is golden and crisp.
07 - Allow turkey legs to rest 5 to 10 minutes before serving; spoon pan juices and vegetables over the portions.