MAIN DISH RECIPES

Slow Cooker French Onion Soup

Updated

This slow cooker French onion soup caramelizes sweet onions right in the crock with butter, balsamic and brown sugar, simmers them with beer, beef stock and thyme, and finishes with Gruyere-topped baguette toasts.

Prep
20 min
Cook
8 hr 35 min
Total
8 hr 55 min
Yield
about 8 servings
Illustration of Slow Cooker French Onion Soup

Properly caramelized onions are the soul of French onion soup, and they usually mean a long stretch of stirring at the stove. In this version from the KitchenSimplicity archive the slow cooker does most of that work: the onions start on high with butter, a splash of balsamic vinegar and a little brown sugar, then the soup simmers low and slow with beef stock, beer and fresh thyme until it is deep, rich and just slightly sweet.

It is an ideal cool-weather project for a weekend or a day at home, and it tastes even better the next day, so you can make it ahead for lunches or a casual supper. Top each bowl with a cheesy broiled baguette toast and serve it with a green salad.

Tips

  • The soup keeps in a covered container in the refrigerator for up to 4 days and freezes well for up to 3 months; make the cheese toasts fresh when you reheat it.
  • A mandoline or a sharp chef’s knife makes quick work of slicing the onions evenly so they caramelize at the same rate.
  • To skip the beer, replace it with an equal amount of stock, or use 1/2 cup dry white wine plus 1/2 cup stock.
  • Swiss, Comte or Havarti can stand in for the Gruyere.

Slow Cooker French Onion Soup

Prep
20 min
Cook
8 hr 35 min
Total
8 hr 55 min
Yield
about 8 servings

Ingredients

  • For the soup:
  • 1/4 cup (4 tablespoons / 57 g) unsalted butter
  • 4 medium sweet onions (such as Vidalia), halved and thinly sliced
  • 3 cloves garlic, minced
  • 2 tablespoons balsamic vinegar
  • 2 tablespoons brown sugar
  • 1/2 teaspoon salt, plus more to taste
  • 3 tablespoons all-purpose flour
  • 1 cup beer, such as a lager or amber ale (or more beef stock)
  • 2 quarts (8 cups) low-sodium beef stock
  • 2 tablespoons chopped fresh thyme (or 1 1/2 teaspoons dried)
  • 1/2 teaspoon black pepper
  • For the cheese toasts:
  • 1 baguette, cut into 1/2-inch slices
  • 6 to 8 ounces (170 to 225 g) Gruyere cheese, sliced or grated (Havarti also works)

Steps

  1. Turn a 6-quart or larger slow cooker to high and add the butter. Cover and let it melt, about 10 minutes.
  2. Add the sliced onions, garlic, balsamic vinegar, brown sugar and salt, and stir until the onions are coated in the butter.
  3. Cover and cook on high for 1 to 1 1/2 hours, stirring about every 15 minutes, until the onions are very soft and turning golden brown. If your slow cooker runs cool, prop the lid open slightly for the last 30 minutes to help them color.
  4. Sprinkle the flour over the onions and stir well. Cover and let it cook for 2 to 3 minutes.
  5. Pour in the beer and stock a little at a time, stirring after each addition so the flour dissolves without lumps. Stir in the thyme and pepper.
  6. Cover, switch the slow cooker to low and cook for 6 to 8 hours, until the soup is dark and full-flavored. Taste and add more salt if needed.
  7. Shortly before serving, heat the broiler and arrange the baguette slices on a baking sheet. Top with the cheese and broil 4 to 6 inches from the heat for 2 to 4 minutes, watching closely, until the cheese is melted, bubbly and golden.
  8. Ladle the soup into bowls and float one or two cheese toasts on top. If you have broiler-safe bowls, you can instead set them on a baking sheet, fill them with soup, top with plain baguette slices and cheese, and broil until the cheese browns.

More recipes: Main Dish Recipes · All recipes