Put roast trimmed of visible fat in large slow cooker. Add beef broth. Put Worcestershire, garlic and spices on top of meat. Add carrots, onion and celery around roast. Cook on low for 7- 8 hours total. Add potatoes about 3 hours into cooking. To thicken gravy, remove about 1 cup of hot liquid, using a separate bowl, combine ¼ cup water and cornstarch until smooth. Mix with a little hot liquid and return mixture to pot. Gently stir, turn crock pot to high and cook until thickened and bubbly. You may want to remove beef before thickening the gravy.