Cook corned beef in Dutch Oven or a large pot, covered with water for 6 hours or until tender. In a large pot, cook potatoes over medium-high heat until tender, about 7 minutes. Drain potatoes and reserve cooking liquid. Place potatoes in a large mixing bowl and mash. Shred the corned beef and add to the large mixing bowl. In a frying pan, sauté onion and celery with butter over medium heat until tender, about 5 minutes. Add vegetable mixture to beef. Add flour and Worcestershire, salt and pepper, to taste. Use reserved cooking liquid, if needed to hold the mixture together. Form mixture into patties. In a frying pan over medium heat, brown patties about 2 minutes per side. Serve with sourdough toast and eggs.