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Vegetarian Slow-Cooker French Onion Soup

French Onion Soup, the Hands-Off Way (a Slow Cooker's Involved!)

Caramelizing onions the traditional way is almost a meditative process, which is also to say it takes time — about about an hour hands-on — to do it properly. So when I learned that a slow cooker could magically transform a pile of onions into deep-brown, concentrated version of themselves, I got very excited.

This means French onion soup is now easily made midweek: caramelize the onions in your slow cooker overnight. In the morning, all you have to do is add water, before letting it finish its magical transformation while you're at work.

Now you could keep everything aside from the cooking method classic, bolstering the onion base with beef stock (instead of water) and topping it all with a cheesy piece of bread, but I decided to take the transformation two steps further. First, I chose water instead of beef stock, which lets the caramelized onions shine and makes it a vegetarian dish. Second, I omitted the bread, instead serving the soup with gruyère crisps for a more refined take that happens to be gluten-free. Overall, it's a different, dare I say elegant, take on the French bistro classic.

No-Stock Slow-Cooker French Onion Soup With Gruyère Crisps

Adapted from The Kitchn and Michael Ruhlman; gruyère crisps recipe adapted from Gourmet


If you're short on time, store-bought parmesan crisps can be substituted for the gruyère crisps.

Vegetarian Slow-Cooker French Onion Soup


  1. 3 pounds yellow onions, peeled, sliced, and cut into quarter moons
  2. 2 tablespoons unsalted butter, melted
  3. 2 tablespoons extra-virgin olive oil
  4. 2 teaspoons kosher salt, plus more to taste
  5. 1 teaspoon freshly ground black pepper, divided
  6. 4 ounces comte or gruyère
  7. 1 tablespoon plus 3/4 teaspoon all-purpose flour
  8. 1/4 cup oloroso or amontillado sherry, optional
  9. 2 tablespoons balsamic vinegar


  1. Add the onions, butter, olive oil, salt, and 1/2 teaspoon pepper to a slow cooker. Cook on low overnight for up to 12 hours. (The onions will slump and caramelize during this time.)
  2. Add 10 cups water and cook on low for 6-8 hours.
  3. Meanwhile, preheat the oven to 375°F. Line a half sheet pan with a Silpat.
  4. Using the largest holes on a box grater, coarsely shred the cheese. Stir together the cheese, flour, and remaining 1/2 teaspoon pepper in a large mixing bowl. Arrange tablespoons of cheese in 6 mounds on the Silpat, stirring the cheese mixture in the bowl occasionally to keep the flour evenly distributed. Flatten each mound slightly with your fingertips to form a 3-inch round.
  5. Bake the crisps until golden, about 8-10 minutes. Cool 2 minutes on the half sheet pan, then carefully transfer each crisp (they are very delicate) with a thin spatula to a rack to cool completely.
  6. When the soup is done cooking, add the sherry (if using) and balsamic. Season to taste with salt, if needed.
  7. Ladle the soup into bowls and serve with 2-3 gruyère crisps per bowl.
Image Source: POPSUGAR Photography/Nicole Perry
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