Blanch salt pork in boiling water 5 minutes. Drain and rinse well; pat dry. Transfer to heavy large skillet and cook over medium flame until lightly browned. Remove from skillet using slotted spoon and reserve for use in salads or other dishes. Increase heat to medium high. Add beef to skillet in batches (do not crowd) and cook until well browned on all sides, turning with spatula. Transfer meat to heavy 2 to 3 quart saucepan. Add onions to skillet and reduce heat slightly and cook until deep golden brown, about 10 minutes, stirring occasionally. Blend in flour and cook about 30 seconds, watching carefully so flour does not burn. Add stout and stir, scraping up any browned bits. Bring mixture to boil. Pour over beef. Blend in vinegar, sugar, parsley, bay leaf and thyme. Cover saucepan and simmer mixture for 30 minutes.
Spread mustard over bread. Press bread into stew. Cover and cook until meat is tender, about 1 hour. Remove bay leaf and discard. Serve immediately.
Serve with boiled potatoes, green salad and beer.