Classic Slow Cooker French Onion Soup

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  • onions, thinly sliced
  • melted butter, preferably unsalted cultured butter
  • granulated sugar or raw cane sugar
  • good-quality beef broth (see tip)
  • salt
  • cracked black peppercorns
  • brandy or Cognac
  • slices baguette, about 1/2 inch thick
  • shredded Swiss or Gruyère cheese

Nothing warms bellies as much as French onion soup locked under a crunchy layer of melted cheese and served in an individual terrine. “That’s the thrill of French onion soup—and breaking through that crusty cheese,” says Judith Finlayson, author of “The 150 Best Slow Cooker Recipes.”

For her dish, she likes to caramelize the onions in raw cane sugar for extra flavor and says the addition of either brandy or Cognac provides a rich flavor. This dish can be made vegetarian by substituting vegetable stock—roasted vegetable stock makes for a good, rich soup.

  1. In slow cooker stoneware, combine onions and butter. Stir well to coat onions thoroughly. Cover and cook on high for 30 minutes to one hour, until onions are softened.
  2. Add sugar and stir well. Place two clean tea towels, each folded in half (so you will have four layers), over the top of the stoneware to absorb moisture and allow the onions to caramelize. Cover with the lid (which will keep the tea towels in place) and cook on high for four hours, stirring two or three times to ensure that onions are browning evenly, replacing towels each time.
  3. Add broth, salt, pepper and brandy or Cognac. Do not replace towels, cover and cook on high for two hours.
  4. Preheat broiler. Ladle soup into ovenproof bowls. Place two slices of baguette on top then sprinkle liberally with cheese. Broil until top is bubbly and brown, 2 to 3 minutes. Serve immediately.

Broth tip: Since it’s important that the broth for this soup be top quality, Finlayson recommends using good-quality homemade broth or enhancing store-bought beef broth.

To improve 8 cups of prepared beef broth, combine it in a large saucepan with 2 carrots, peeled and coarsely chopped, 1 tsp. celery seed, 1 tsp. cracked black peppercorns, 1/2 tsp. dried thyme, 4 parsley sprigs, 1 bay leaf, and 1 cup white wine. Bring to a boil, then simmer, covered, for 30 minutes and strain.

A food-writer and journalist, Judith Finlayson has spent much of her life seeking out memorable food experiences. Her other best-selling cookbooks include The Healthy Slow Cooker, 175 Essential Slow Cooker Classics, The Complete Whole Grains Cookbook, and Delicious and Dependable Slow Cooker. She lives with her husband and daughter in Toronto.  Judith also has 750 Best Appetizer Recipes releasing this fall. Photo credit: