In a small bowl, combine salt, paprika, garlic powder, white pepper, thyme, sage, mustard, and dill. Set aside.
Chicken Thighs
Using a paper towel, pat chicken thighs dry. Place chicken thighs in a cast iron pan and drizzle with oil. Turn thighs to coat completely with oil. Arrange thighs in pan skin side up. Sprinkle with spice mixture. Scatter the fresh rosemary leaves over the top of the chicken.
Bake chicken in preheated oven for 45 minutes, or until juices run clear when pierced with a fork.
Notes
Chicken is done when an instant-read thermometer inserted horizontally in the thickest part of the thighs registers 165°F. The temperature will rise about 5°F after removing from the oven, so it is best to remove the thighs from the oven when the internal temperature is slightly less than the desired temperature.