Cut core from cabbage; rinse.
In medium glass bowl, heat cover with plastic wrap, at high4 to 5 minutes.
Remove 10 leaves; cut out hard center rib from each leaf (make a V-shape cut).
Into medium bowl crumble ground beef and combine with onions, 1/2 tomato sauce, rice, salt and pepper.
To stuff cabbage, place beef-rice filling in cabbage leaf; roll up, folding edges in.
Arrange seam-side down in 2-quart oblong dish.
Blend tomato sauce with brown sugar and vinegar.
Pour over rolls.