Crockpot French Onion Soup
Rich, deeply caramelized onions simmered in a flavorful beef broth with thyme, garlic, and a splash of wine — all topped with crusty bread and melted Gruyère. This slow cooker version gives you the same depth as the stove-top classic but without the constant stirring.
🧡 Why You’ll Love It
- Classic bistro flavor with minimal hands-on work
- Slow cooker handles the caramelizing for you
- Make-ahead and freezer-friendly
- Elegant enough for holidays, simple enough for weeknights
- Customizable with different cheeses or bread toppings
🧂 Ingredients
For the Soup
- 4 large yellow onions (about 2½–3 lbs), thinly sliced
- 3 Tbsp unsalted butter
- 1 Tbsp olive oil
- 1 tsp salt
- ½ tsp sugar (helps onions caramelize)
- 4 garlic cloves, minced
- 6 cups beef broth (low sodium preferred)
- ½ cup dry white wine or dry sherry (optional but classic)
- 1 tsp Worcestershire sauce
- 1 sprig fresh thyme (or ½ tsp dried)
- 1 bay leaf
- ½ tsp black pepper
For Serving
- 1 baguette, sliced and lightly toasted
- 1½ cups shredded Gruyère (or Swiss or Provolone)
- Fresh thyme or parsley, for garnish
Recommended tools
- 6-quart slow cooker
- Mandoline slicer for quick, even onion slicing
- Soup crocks or oven-safe bowls
- Kitchen torch for broiling cheese if you’re not using the oven
🍳 Steps
- Caramelize the onions (hands-off method):
Add sliced onions, butter, olive oil, salt, and sugar to your slow cooker. Stir to coat.
Cover and cook on HIGH for 8–9 hours, stirring once or twice if you can. The onions should turn deep golden brown and soft.(If you’re short on time, you can pre-caramelize onions on the stovetop for 20–25 minutes before adding them — this shortens the slow cooker time to about 5 hours total.) - Build the soup:
Once the onions are golden, stir in garlic, thyme, bay leaf, Worcestershire, pepper, broth, and wine (if using).
Cover and cook on LOW for 4–6 hours or HIGH for 2–3 hours, until the flavors meld. - Finish and taste:
Discard thyme sprig and bay leaf. Taste and adjust with salt, pepper, or an extra splash of Worcestershire if needed. - Prepare bread topping:
Slice and lightly toast baguette slices under the broiler or in a toaster oven. - Serve:
Ladle soup into oven-safe bowls. Top each with 1–2 baguette slices and a handful of Gruyère.
Broil 2–4 minutes until cheese bubbles and turns golden.
(If your bowls aren’t oven-safe, melt the cheese separately under the broiler and top the soup afterward.) - Garnish and enjoy:
Sprinkle with thyme or parsley and serve immediately.
💡 Helpful Tips & Substitutions
- Onion type: Yellow onions are ideal — they caramelize evenly and balance sweet and savory notes. Avoid red onions (too sharp) or white (too mild).
- Broth matters: Use good-quality beef broth or stock; it’s the backbone of flavor. You can mix beef and chicken broth for a lighter taste.
- Wine substitutes: If avoiding alcohol, replace wine with ¼ cup balsamic vinegar or ¼ cup extra broth + 1 tsp apple cider vinegar.
- Cheese options: Gruyère melts best; Swiss, provolone, or mozzarella are fine swaps.
- Make it vegetarian: Use vegetable broth and a splash of soy sauce for umami depth.
- Make it creamy: Add ¼ cup heavy cream before serving for a richer French onion bisque.
🎁 Serving Ideas
- Serve as a cozy first course for a holiday meal.
- Pair with a crisp green salad or roasted vegetables.
- Make it the main course with a simple side of steak tips, roast turkey breast, or grilled sausage.
- Garnish with extra thyme and cracked pepper for a polished look.
🕒 Make-Ahead & Storage
Prep ahead:
- Caramelize onions a day before; refrigerate. When ready, add broth and seasonings and cook for 4–6 hours on LOW.
Storage:
- Store soup (without bread or cheese) up to 4 days in the fridge.
- Freeze up to 3 months — thaw overnight before reheating.
Reheat:
- Reheat gently on the stovetop or in a slow cooker.
- Toast fresh baguette and add cheese just before serving.
This Crockpot French Onion Soup gives you all the rich, comforting flavor of the traditional stovetop version — with none of the babysitting. It’s elegant enough for a Christmas Eve dinner, but simple enough for a cozy weekend at home.