Weeknight French Onion Soup

Use your slow cooker to make warm and cozy french onion soup a reality during the week.

photo of a bowl of French Onion Soup

French Onion Soup

I shared a recipe for crockpot mashed potatoes back in November and in that post, I mentioned something about not loving my crockpot. Right after that, I spun around and asked Santa to bring me a shiny new slow cooker for Christmas (my old one was olllld… 17 years old, I think) because, seriously, why haven’t I embraced crockpot cooking in the six-plus years I’ve been writing this blog?

So I decided to challenge myself and get back on the slow cooker horse starting with a classic French onion soup after learning that a slow cooker is a great hands-off way to caramelize onions. Normally, you’d have to spend at the least 45 minutes to an hour standing over the stove to get the same result making French onion soup a great dish to make on the weekend, but a terrible one for mid-week. Who has time to caramelize onions on a Tuesday night?

How to Caramelize Onions in a Slow Cooker

The best part about using your slow cooker to caramelize the onions is that it’s a hands-off operation. The trade-off is that you won’t get deeply golden browned onions that you would otherwise get if you caramelized them on the stove, but they still come out the slow cooker tender and sweet. The trade-off is worth it for me to be able to have a cozy bowl of French onion soup on a random Tuesday that would otherwise require a half-day off work if I made it from start to finish on the stove.

  • I like to use white onions for this recipe and you’ll want to slice two pounds of them.
  • Place them in the slow cooker along with butter and some sprigs of fresh thyme.
  • Cook them on low for 10 to 12 hours. I like to do this the night before I want to have the soup for dinner. I stir them after they’ve been in the slow cooker for three hours or so. The next morning I give them another stir an hour or so before they’re done.
  • Transfer the cooked onions (be sure to remove the thyme springs!) to a container along with all of the liquid in the slow cooker. Pop them in the fridge until you’re ready to make the soup.

photo of a bowl filled with soup

How to Make French Onion Soup

Once the slow cooker caramelized onions are done the soup comes together in about 30 minutes.

  • Warm the onions and their liquid over medium heat in a pot.
  • Add some white wine and simmer it with the onions.
  • Sprinkle some flour over the top and stir to coat the onions in it. The flour will help thicken the soup a bit.
  • Add the beef broth, some Worcestershire sauce, and a bay leaf and bring the soup to a boil and reduce the heat to maintain a simmer.
  • While the soup is simmering, toast some sliced bread (I like to use a thin baguette) under the broiler and grate some gruyere cheese.
  • Ladle the soup into oven-safe bowls and place them on a sheet pan. Top each soup bowl with a few slices of toasted bread and pile some gruyere cheese on top. Transfer them under the broil just until the cheese is melted and bubbling.

overhead photo of bowls of french onion soup being assembled

Hello, weeknight French onion soup.

The toast soaks up all the brothy goodness and the cheese – that cheese! I am in love with the ooey-gooey gruyere cheese. One bite and you’ll feel like you’re sitting in a French bistro far, far away from your normal it’s-just-another-Tuesday-night situation.

All thanks to a slow cooker.

overhead photo of two bowls of French Onion soup topped with toasted bread and melted gruyere cheese

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Weeknight French Onion Soup

Classic French onion soup made easy thanks to the slow cooker. You can caramelize the onions ahead of time in the slow cooker so all you need is 30 minutes the next day to add the finishing touches. Perfect for a weeknight supper!

  • Author: April @ Girl Gone Gourmet
  • Prep Time: 10 minutes
  • Cook Time: 12 hours 30 minutes
  • Total Time: 12 hours 40 minutes
  • Yield: 4 servings 1x
  • Category: Soups & Stews
  • Method: Slow Cooker
  • Cuisine: French

Ingredients

Scale

For the Caramelized Onions

  • 2 pounds white onions, thinly sliced
  • 1/4 cup unsalted butter, cut into chunks
  • 4 sprigs fresh thyme
  • 1 teaspoon salt

For the Soup

  • 1/2 cup dry white wine
  • 1 tablespoon flour
  • 1 (32-oz) box of beef broth (see note)
  • 1 bay leaf
  • 1 tablespoon Worcestershire sauce
  • 8 slices French bread (see note), toasted
  • 8 ounces Gruyere cheese, grated

Instructions

  • Place the sliced onions, butter, thyme, and salt into the slow cooker. Toss it all together and then cover and cook on low for 10-12 hours. I stir them a couple of times as they are cooking. Once the onions have cooked discard the thyme sprigs and transfer the onions (and all of the liquid) to a bowl. Cover and refrigerate until you’re ready to make the soup.
  • To make the soup. First, heat the onions and all of their liquid over medium heat in a 5-quart pot. Add the wine and simmer it for a few minutes with the onions. Sprinkle one tablespoon of flour over the top and give it all a stir. Add the beef stock, bay leaf, and Worcestershire sauce to the pot. Raise the heat until the soup is at a strong simmer and then lower the heat to maintain a gentle simmer.
  • Once the soup has simmered for 20 to 30 minutes, check the seasoning and add additional salt, if needed. Ladle the soup into oven-safe bowls.
  • Place bread slices on top of each soup and top each with the grated cheese. Place the bowls on a baking sheet lined with tin foil. Place the bowls under the broiler for a few minutes (keep a close eye on them) until the cheese is melted and bubbly. Remove and serve immediately.

Notes

  • I used regular beef broth for this recipe, so if you use low-sodium beef broth you made need to adjust the salt level of your soup so be sure to taste it while it’s simmering to make any adjustments.
  • I used eight slices of bread from a thin baguette which was approximately 16 ounces of bread. Depending on the type of bread you use the nutrition estimate may vary.

Nutrition

  • Calories: 785
  • Sugar: 16g
  • Fat: 33.1g
  • Carbohydrates: 84g
  • Fiber: 6.6g
  • Protein: 34.8g

Keywords: easy french onion soup, slow cooker french onion soup

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8 Comments

    1. Hi Anne – Thanks so much for asking! I meant to update that in the recipe before publishing — it’s there now, and, yes, you will need a 32 ounce box of broth. I think I still have some holiday fog to shake off 🙂

  1. April, one of my absolute favourite all time soups, and now I can make it in my crockpot! Perfect, looks absolutely delicious. Can’t wait to try it.

  2. Can you put the crockpot carafe with the onions in the fridge the night before and pull it out cold and plug it in the actual crockpot machine in the morning? I didn’t know if going from hot to cold would crack it.

    1. Hi Sandra, I’m not sure about that, so if you have the book that came with your slow cooker I would check that. Or maybe check online with the manufacturer — hope that helps!

  3. My son’s favorite soup is French Onion soup. He said this beats any he has had before. Going to be making this soup again. Thanks April.

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