01 - Set oven temperature to 300°F.
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 create an even paste.
04 - Rub the seasoning paste uniformly over each turkey leg.
05 - Spread sliced onion, carrots, celery chunks, and smashed garlic cloves evenly across the bottom of a large roasting pan.
06 - Place the seasoned turkey legs atop the bed of vegetables.
07 - Pour the broth into the roasting pan without drenching the turkey legs.
08 - Cover the roasting pan tightly with aluminum foil and roast for 2 hours.
09 - Remove foil; if desired, brush turkey legs with melted butter. Increase oven temperature to 400°F and roast uncovered for 25–30 minutes until skin is golden, crisp, and internal temperature reaches 165°F.
10 - Let turkey legs rest for 10 minutes before serving.