Combine garlic, rosemary, fennel, salt, pepper and 1 tablespoon olive oil in small bowl. Rub over meat. Wrap and refrigerate 4 hours or overnight.
One hour before roasting remove pork from refrigerator. Preheat oven to 400 degrees F. Heat olive oil and butter in roasting pan over medium-high heat. Add pork and cook, turning, until browned on all sides, 10 minutes. Transfer to oven.
Roast, turning after 30 minutes, until meat thermometer inserted in thickest part registers 160 degrees F, 45-55 minutes. Transfer roast to platter; keep warm. Let stand 10 minutes before slicing.