Mix onions and margarine in 3½- to 6-quart slow cooker.
Cover and cook on high heat setting 30 to 35 minutes or until onions begin to slightly brown around edges.
Mix flour, Worcestershire sauce, sugar and pepper. Stir flour mixture and broth into onions. Cover and cook on low heat setting 7 to 9 hours (or high heat setting 3 to 4 hours) or until onions are very tender.
Prepare Cheesy Broiled French Bread. Place 1 slice bread on top of each bowl of soup. Serve immediately.
Recipe by A Frugal Chick at https://www.afrugalchick.com/slow-cooker-french-onion-soup/