Preheat oven to 325°F.
Combine the dry mustard, salt, pepper and flour.
Dredge the round steak in the flour mixture.
Brown the steak well in the frying fat.
Transfer the steak to a roasting pan.
Top with the sliced onions, diced carrots, Worcestershire sauce, brown sugar and canned tomatoes.
Cover and bake for 1½–2 hours.