Crumble beef into 4-5 quart dutch oven. Add onions & cook over med high heat 5-6 minutes, stirring often, until beef is lightly browned. Quarter & core cabbage. Cut crosswise in 1" wide strips, should have about 8 cups. Add to meat mixture, cover & cook over med heat 5-7 minutes, stirring occasionally, until the cabbage wilts. Stir in tomatoes, sugar, vinegar & salt. Bring to a boil, reduce heat, cover & simmer, stirring occasionally, 10 minutes or until cabbage is tender.