Brown brisket on both sides in a large Dutch oven over medium-high heat, browning fat side first. Add salt, pepper, 2 cu. water, and hot sauce, if desired. Reduce heat to low. Cover an d simmer 1 hour. Do not drain.
Melt butter in a large skillet over medium-high heat. Add onion; saute 8 minutes or until tender. Stir in ketchup, tomato soup, lemon juice, and brown sugar, mixing well.
Pour onion mixture over brisket in Dutch oven. Cover and simmer 2-1/2 hours or until meat is very tender, stirring occasionally.
Transfer brisket to a warm platter and let stand 10 minutes; cut diagonnaly across grain into thin slices. Serve with remaining sauce.