Combine the horseradish and mustard and spread half of it over beef. Stir together the brown sugar and broth, pour over the corned beef. Cover the dutch oven and place in oven. Save remaining horseradish and mustard for dipping.
After the corned beef has roasted for 1 hour, remove the beef, place vegetables in the broth, add beef back to the Dutch Oven. Add more broth if needed.