Season the beef with mustard powder, salt and pepper.
In a large stock pot, add meat, onion and remaining spices. Cover with water and add vinegar.
Bring to a boil, then reduce heat to medium low and simmer for 1 hour.
Add the cabbage to the pot and cook for an additional 1-2 hours until the meat and cabbage are tender.
Slice beef thinly across the grain and serve with horseradish.