Caramelized onions are one of those kitchen transformations that never fails to delight: sharp, raw onions slowly become meltingly tender, sweet, and deeply savory. I use them constantly—on sandwiches, pizzas, salads, in pasta, dips, breads, and stuffing. Because they take a long time to make, I prepare large batches so I always have a jar or two ready for whatever dish I’m planning.
My preferred method is the slow cooker. It’s the perfect vessel for caramelizing onions for several reasons:
- It maintains a low, steady temperature so the onions can transform without constant attention. After an initial stir at one hour and another at three hours, they’re happy to cook unattended.
- Slow cookers hold a large quantity, so you can make a substantial batch—which makes sense when you’re investing that much time.
- If you want French onion soup, you can leave half the onions in the slow cooker and add the remaining soup ingredients directly to the pot, warming everything together while you prepare the croutons. One-pot soup with minimal cleanup is a big win.
- Yes, the house smells amazingly of caramelizing onions while they cook. If the aroma is an issue, I sometimes plug the slow cooker in outdoors. It’s an easy trick if you have the space and want to avoid driving the household into a state of hungry anticipation.
Easy French Onion Soup from Caramelized Onions
One of the quickest ways to turn a batch of slow-cooked onions into a comforting meal is to use half the caramelized onions for French onion soup. Combine the onions with beef and chicken broth, add a splash of red wine if you like, and heat through. Toast thick slices of French bread until crisp, float a crouton on each bowl of hot soup, top with Swiss cheese, and broil until the cheese is melted, bubbly, and browned.
Other Ways to Use Caramelized Onions
- Stir into mashed potatoes for a rich, savory boost.
- Pair with feta on pizza.
- Add to grilled cheese sandwiches for an incredible flavor upgrade.
- Top baked potatoes as a low-fat, high-flavor garnish.
- Mix with softened cream cheese and cracked black pepper for a delicious vegetable dip.
- Serve on toasted bread with goat cheese or cream cheese for an elegant appetizer.
- Toss with freshly cooked pasta and finish with grated Parmesan.
- Roll into bread dough for a savory filled loaf or buns.
- Scatter over focaccia before baking, then serve wedges with soup.
- Layer on deli sandwiches for an extra-special finish.
- Offer as a condiment alongside grilled steak, chicken, or pork.
What’s your favorite way to enjoy caramelized onions?
Slow-Cooker Caramelized Onions & French Onion Soup
Rebecca Lindamood
Ingredients
For the Slow Cooker Caramelized Onions
- 12 small to medium yellow onions
- 3 medium red onions
- 6 tablespoons olive oil
- 1/2 teaspoon kosher salt
- 1/2 teaspoon dried thyme
For the French Onion Soup:
- 1 1/2 cups beef broth
- 1 1/2 cups chicken broth
- kosher salt and black pepper to taste
- 6-8 slices French bread 1 to 1 1/2-inches thick
- olive oil for drizzling
- 6-8 thin slices Swiss cheese or 1/4 pound grated Swiss, more to taste
Instructions
To Make the Slow Cooker Caramelized Onions:
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Halve, peel, and thinly slice all the onions. Drizzle 2 tablespoons of olive oil into the slow-cooker crock. Add about half the onions, sprinkle half the salt, drizzle another 2 tablespoons of oil, then add the remaining onions, salt, and oil. Sprinkle the thyme over everything and toss with tongs so the onions are evenly coated. Cover, set the cooker to HIGH, and cook for 9–10 hours, stirring and turning the onions after 1 hour and again after 3 hours. After those stirs you likely won’t need to tend them unless your slow cooker runs hot; if it does, stir every couple of hours to prevent scorching. When the onions are deep golden to medium brown, turn the cooker off and portion the onions into freezer-safe containers. I usually reserve one large container for soup and two smaller ones for pizzas, sandwiches, and other uses.
To Make the French Onion Soup:
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Preheat the oven to 400°F.
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Either transfer half the caramelized onions to a pot or leave them in the slow cooker and add the beef and chicken broths. Heat over high until steaming.
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Drizzle the bread slices with olive oil and toast them in the preheated oven for about 6 minutes, flipping once, until golden and crisp. Trim to fit bowls if needed.
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Taste the heated soup and adjust with salt and pepper. Ladle into broiler-safe bowls, top each with one or two croutons, and add a slice or a generous handful of Swiss cheese. Broil until the cheese is melted, bubbly, and lightly browned. Serve immediately.
Nutrition
Nutritional information is an estimate and provided as a courtesy. Calculate nutrition with the exact ingredients you use if needed.
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