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How to Caramelize Onions in a Slow Cooker (and a French Onion Soup Recipe)

Happy soup season! Is there anything more comforting and delicious than French Onion Soup? I love it any time of year (yes, even in the summer). But when the days get chilly, a cup of hot French Onion Soup and a crackling fire are the perfect companions.

In this version, we make it in a slow cooker in a two-step process. First, we caramelize the onions in the slow cooker. That’s right, directly in the slow cooker. This creates the chemical reaction similar to stovetop caramelization, but without having to babysit the onions as they cook down. You simply slice the onions, either by hand or by a MUCH easier, quicker method – with a food processor, and place in the slow cooker crock. Add a little olive oil (or butter, if you prefer), garlic, and let it sit for 6-7 hours on HIGH, or 10-12 hours on LOW. You’ll want the onions to be a deep, golden brown (but not too dark because they can become bitter). You can also add a little sugar if you want a sweeter carmalization. I have even thrown in a few sliced shallots with my onions to give it a nice balance of sweet with a bright flavor different than an onion.

After the onions are caramelized, just add the remainder of the ingredients for the soup and continue to cook in the crock for about another hour. While it cooks, you can prepare the bread and cheese topping (don’t skimp on this crunchy gooey step – some think it’s the best part of French Onion Soup).

This soup is absolutely, positively, definitely comfort in a bowl.

Here’s a tip from our Test Kitchen: Caramelized onions don’t have to be used right away. Save them in individual portion packs for burger or sandwich toppings, or throw them into soups, stews or other recipes as needed. You can even portion the cooked onions in ice cube trays and freeze. Then, pop out the frozen onions and store in individual containers or bags until you’re ready to use them.

Slow Cooker French Onion Soup

Yield: Serves 8
Author: Hamilton Beach Test Kitchen


  • 3 pounds onions, halved
  • 2 cloves garlic, minced
  • 1 tablespoon olive oil
  • 8 cups beef stock
  • 1 cup dry white wine
  • 1 1/2 teaspoons Worcestershire sauce
  • 2 sprigs fresh thyme
  • 1 teaspoon sugar, optional
  • 1 1/2 teaspoons salt
  • 1/2 to 3/4 teaspoon pepper
  • French bread
  • 2 tablespoons butter, softened
  • 1 cup grated gruyere cheese


  1. In food processor using slicing disk, slice onions.
  2. In slow cooker crock, stir onion slices and garlic with olive oil until well coated.
  3. Cover and cook on HIGH for 6 to 7 hours or LOW for 10 to 12 hours until onions are carmelized. Stir once or twice during cooking.
  4. Add beef stock, wine, Worcestershire sauce, salt and pepper. Cover and cook on HIGH for 1 hour or until heated through.
  5. While soup heats, cut bread to fit ramekins or oven-safe bowls. Spread butter on bread and toast under broiler.
  6. Ladle soup in ramekins or bowls. Top with bread and sprinkle generously with cheese. Place under broiler to melt cheese.

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  1. I put the onions in the slow cooker last night. I just got up and they look perfect. I may never caramelize onions any other way again. Thanks for the awesome tip!

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