Preheat oven to 450°.
Place roast on a broiler pan coated with cooking spray. Combine thyme, salt, pepper, and 4 garlic cloves; rub over roast. Bake at 450° for 45 minutes.
Reduce heat to 350° (do not remove roast from oven). Bake roast at 350° for 1 hour and 20 minutes or until a thermometer registers 145° (medium-rare) or until desired degree of doneness. Let stand 10 minutes before slicing. Garnish with parsley and roasted garlic, if desired.