Brown brisket on both sides in a large Dutch oven, browning fat side first. Add salt, pepper, hot sauce, if desired, and water. Cover and simmer 1 hour. Do not drain.
Sauté chopped onion in shortening in a large skillet until tender. Stir in catsup, tomato soup, lemon juice, and brown sugar, mixing well.
Pour mixture over brisket in Dutch oven. Cover and simmer an additional 1 hour and 15 minutes or until meat is very tender, stirring occasionally.
Transfer brisket to a warm platter; cut diagonally across the grain into thin slices. Serve with sauce remaining in Dutch oven.