01 - Set the oven to 300°F to prepare for slow roasting.
02 - Pat the turkey legs dry using paper towels.
03 - Combine olive oil, kosher salt, black pepper, smoked paprika, garlic powder, thyme, rosemary, and onion powder in a small bowl to form a paste.
04 - Rub the seasoning paste evenly over all sides of the turkey legs.
05 - Spread the sliced onion, carrots, celery, and smashed garlic cloves evenly in the bottom of a large roasting pan.
06 - Place the seasoned turkey legs on top of the arranged vegetables.
07 - Pour the chicken or turkey broth into the roasting pan around the vegetables, avoiding pouring directly over the turkey legs.
08 - Cover the pan tightly with aluminum foil and roast for 2 hours to slowly cook the turkey.
09 - Remove the foil, optionally brush turkey legs with melted butter, increase oven temperature to 400°F, and roast uncovered for 25 to 30 minutes until the skin is golden and internal temperature reaches 165°F.
10 - Allow the turkey legs to rest for 10 minutes before serving to redistribute juices.