Step 1: Prepare the Onions
Begin by slicing four large onions. The key to a great French onion soup is to cut the onions into uniform slices to ensure even cooking. Place the sliced onions into the bottom of a 6-quart slow cooker.
Step 2: Add Butter, Sugar, and Salt
Add 2 tablespoons of butter, 1 teaspoon of sugar, and 1 1/2 teaspoons of salt to the slow cooker with the onions. The sugar helps to enhance the caramelization process, while the butter adds richness.
Step 3: Slow Cook the Onions
Cover the slow cooker and cook the onions on high for 7 hours, or until they are soft and brown. This long cooking time allows the onions to develop a deep, caramelized flavor that is essential for authentic French onion soup.
Step 4: Add Broth, Sherry, and Thyme
After the onions are beautifully caramelized, add 2 quarts of no sodium added beef broth, 1/4 cup of sherry, 2 sprigs of fresh thyme, and pepper to taste. Cover the slow cooker and continue to cook on high for an additional hour. This step melds all the flavors together, creating a rich and savory broth.
Step 5: Prepare the Toppings
While the soup is finishing in the slow cooker, prepare your toppings. Slice your bread of choice or use croutons. For an authentic touch, use French baguette slices. Slice 8 ounces of Gruyere cheese (or Swiss cheese if you prefer).
Step 6: Serve the Soup
To serve, ladle the soup into ovenproof mugs or bowls. Place a slice of bread (or croutons) on top of each serving. Add a generous slice of Gruyere cheese over the bread. For an extra cheesy experience, broil the mugs under a broiler for a few minutes until the cheese is bubbly and golden brown.
Step 7: Optional Cheese Melting
For those who love their cheese extra melty, cook the soup with the cheese topping for an additional 15 minutes in the slow cooker before serving. This will allow the cheese to melt further into the soup, enhancing its flavor and texture.
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