Trim fat from roast; brown in skillet on all sides in hot oil. Drain well. In 3 1/2 to 4 quart crock pot place first onion, then sweet potatoes. Place roast in top of vegetables, cut if necessary to fit. Combine beef broth, celery salt, salt, and cinnamon. Pour over all. Cover. Cook on low 10-12 hours or high 4-5 hours. To serve, transfer roast and vegetables to platter. Reserve juices. Measure 1 cup; make gravy by stirring cornstarch in cold water; add juices. Cook and stir for 2 minutes, until thickened and bubbly. 6 servings.