In a mortar and pestle, grind the fennel, pepper, salt, garlic, orange zest and rosemary into a rough powder. Rub over the pork and leave to marinate for at least 1 hour.
Place a really large, heavy pan over high heat for 2 minutes. Fry the rosemary sprig to crisp slightly, then remove and set aside. Rub pork chops with olive oil and place in pan. Cook for 3 minutes on the first side then flip and season with salt. Cook for a further 3 minutes on the second side then rest on a plate. Add the orange juice to the pan and bring to the boil. At the last minute, stir through the butter. Briefly replace the pork chops in the pan and swirl them in the sauce. Remove pork chops and place on a plate. Simmer the sauce, scrape the pan and pour the juices over the chops to serve, dropping the fried rosemary on top.
These chops work really well with my hasselback potatoes.