Pour vegetable oil into a large casserole dish over medium-high heat. Season the roast with salt and black pepper. Brown the meat on both sides in the hot oil then transfer to a plate.
Stir carrots, celery and onion into the casserole dish then cook and stir until vegetables start to release their juices, about 3 minutes; loosen any brown flavour bits on the bottom of the dish. Add butter then cook until the onions are translucent, about 5 minutes. Then sprinkle in rosemary, stir the vegetables then return the roast to the dish. Cover the casserole dish with a lid.
Roast in the preheated oven until the roast is tender, about 2 1/2 to 3 hours. Season vegetables with additional salt and black pepper, if desired.