In your slow cooker add the butter and onions. Cover and cook on HIGH until onions brown around the edges, about 30-35 minutes.
Meanwhile, mix together the flour, Worcestershire sauce, sugar, and pepper. Stir the flour mixture into the onions. Add the brother and cover and cook until onions are very tender, about 7-9 hours on LOW.
Once the soup is done, preheat your broiler to high. Place shredded cheese on the pieces of bread and broil until melted. Place a piece of bread on each bowl of soup and serve.
Notes
Don't have all day? Cook this soup on HIGH for 4-5 hours.
Use a wooden spoon to get all of the browned pieces at the bottom of the pot when adding the flour. That's the best stuff!
Perfect Pairing
Serve this Slow Cooker French Onion Soup with Kentucky Mulled Cider.
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