French Onion Soup

French onion soup is basically caramelized onions transformed into a rich, flavorful broth topped with cheesy bread. The French truly nailed comfort food!

Caramelizing onions does take some patience, but trust me, it’s totally worth it. Those golden, sweet onions create an amazing flavor base for this classic French onion soup. Want a hands-off approach? I’ll show you how to caramelize onions in a slow cooker too!

French onion soup might just be one of the most legendary soups out there. And guess what? It only needs a few basic ingredients: butter, onions, flour, and broth or stock.

The secret is in slowly caramelizing those onions for at least 40 minutes to develop that rich, sweet flavor. And don’t forget the crowning touch — that ooey-gooey melted cheese toast! Because honestly, French onion soup without the cheesy toast? That’s just onion soup. Yawn!

If you’re a fan of caramelized onions and melted cheese, you’re going to love this French onion soup. It takes a short list of humble ingredients — onions, butter, flour, and stock — and turns them into a bowl full of deep, rich, and comforting flavors. The star is those slow-cooked golden onions and, of course, the cheesy toast that finishes the dish beautifully.

Keep reading for a step-by-step stovetop method that gets the onions perfectly caramelized (plan on about 45–60 minutes for a big batch), plus an easy slow-cooker shortcut if you’re short on time. I’ll walk you through making the broth, prepping the cheesy toast, and plating it all up. You’ll also find a handy recipe video, notes on which broths and cheeses work best, and tips for making this ahead, storing leftovers, and reheating.

Whether you’re whipping this up for a cozy weeknight meal, a crowd, or prepping ahead to save stress, I’ll guide you through simple little tips so you can get restaurant-quality French onion soup without the fuss.

Why You’ll Love It

This recipe shines because the onions are caramelized to deep, sweet perfection, giving the soup a rich, savory base. Then the melted cheese on toast adds a melty, crispy touch — it’s basically caramelized onion in the yummiest soup form. Using everyday pantry staples (onions, butter, flour, stock), this recipe gives you big, bold flavor. You can make the whole thing on the stove for the best taste or do the onion caramelizing in the slow cooker for convenience, finishing the soup on the stove. It’s perfect for cozy dinners, make-ahead portions, and feeding a crowd—much like Cabbage Roll Soup.

Ingredient Checklist

• 100 g / 3.5oz unsalted butter
• 1.25 kg / 2.5 lb brown / yellow onions, peeled, halved, thinly sliced top to bottom (Note 1)
• 3/4 cup (185ml) dry white wine, optional (Note 2)
• 2 tbsp flour, plain / all purpose
• 1.5 litres / 6 cups / 1.5 quarts good quality beef broth./stock OR chicken, low sodium/salt reduced (Note 3)
• 2 dried bay leaves (or 3 fresh) (optional)
• 3 sprigs fresh thyme (optional)
• Salt and pepper
• 6 – 8 slices French baguette or other softish bread (Note 4)
• 100 g / 3.5 oz gruyere or mozzarella cheese, or other melting cheese of choice
• Fresh parsley or thyme leaves, for garnish (optional)

How to Make It

1. Melt butter in a heavy-based casserole over medium heat, add sliced onions and stir to coat.
2. Lower heat to medium-low and cook about 30 minutes, stirring every few minutes, until onions soften and become translucent.

3. Increase heat to medium or medium-high, sprinkle salt, and cook 20–30 minutes more, stirring often until onions are deeply golden and sweet.

4. Slow-cooker option (optional): toss sliced onions with 2 tbsp melted butter, cook on LOW for 10 hours, then transfer most onions and some jus to a pot with 2 tbsp butter and cook on medium-high 10–15 minutes to finish caramelising.
5. Pour in dry white wine (if using) and simmer rapidly 2 minutes, scraping up browned bits from the pot bottom.
6. Sprinkle flour over the onions and cook 1 minute to remove raw flour taste.
7. Pour in beef (or chicken/vegetable) broth and add thyme sprigs and bay leaves.
8. Cover, reduce heat to low, and simmer gently for 30 minutes to blend flavors.
9. Taste and season with salt and pepper; remove thyme sprigs and bay leaves.
10. Preheat grill/broiler to high and toast bread slices on both sides until lightly golden.
11. Top toasted bread with cheese and grill again until the cheese melts and starts to brown.

Pro Tips for Success

The caramelized onions are the soul of this French onion soup — well, along with the cheesy toast! Classic stove-top caramelizing takes about 45 minutes for a big batch like this.

It’s not hard or exhausting though. Mostly you’re cooking low and slow, just remembering to stir every few minutes.

It’s perfect to make while you’re tidying up or prepping other dishes. I use a 24 cm (10 inch) cast iron pan filled to the brim with onions, and it took nearly an hour to caramelize. If you have a wider pan, it can be a bit quicker — closer to 45 minutes.

If that sounds like too much, don’t worry — I’ve got an easy slow cooker shortcut coming right up.

Besides the onions, the soup itself is quick and breezy. Deglazing the pot with a splash of wine clears up those tasty stuck bits — see it in action in this Slow Cooker Pot Roast recipe. A pinch of flour thickens the broth just a touch. Then, a good dose of broth and some optional fresh herbs take it all home.

GOOD BEEF BROTH IS A MUST!

If you’re buying broth, which I often do for ease, choose a good quality beef broth or stock. Most mainstream brands I find at Australian supermarkets don’t cut it flavor-wise.

If you can’t get a high-quality beef broth, go with chicken or vegetable stock instead. I’ve found those usually taste better than poor-quality beef stock. Beef broth is great for gravies and stews, but here — where it really stars — quality makes all the difference.

Really, I’m not about keeping a special oven-safe bowl just for this soup. While it’s beautiful to serve bubbling hot with cheese melting right in the bowl, I prefer making grilled cheese separately.

That way, the bread keeps its crunch and doesn’t get soggy soaking up soup before it reaches the table.

If you’re buying broth, which I often do for ease, choose a good quality beef broth or stock. Most mainstream brands I find at Australian supermarkets don’t cut it flavor-wise.

If you can’t get a high-quality beef broth, go with chicken or vegetable stock instead. I’ve found those usually taste better than poor-quality beef stock. Beef broth is great for gravies and stews, but here — where it really stars — quality makes all the difference.

Flavor Swaps and Add-Ins

Yes, you absolutely can use a slow cooker—and if you love these flavors in a set-it-and-forget dinner, try Crockpot Creamy French Onion Chicken and Orzo.

A reader shared this method with me, and I’ve found it’s a total lifesaver. Super hands-off — just toss onions with butter or oil in the slow cooker and leave them to cook on LOW for 10 hours.

This shortcut gets you about 75% of the flavor and color you want. The onions brown nicely but don’t develop that deep caramelized flavor you get on the stove.

So you’ll still want to finish them off by cooking on the stove for about 10–15 minutes to bring that flavor home. It’s still way faster and easier than doing it all on the stove for nearly an hour!

Plus, no struggling to handle a giant pot overflowing with onions — which I can totally relate to.

Storage and Make-Ahead

Refrigerate cooled soup (without bread) in an airtight container for up to 3–4 days.

Freeze soup (again, without bread) for up to 3 months. Thaw overnight in the fridge before reheating. If you like having soups ready to reheat, Roasted Tomato Soup and Creamy Roasted Pumpkin Soup are great make-ahead options.

To reheat, warm gently on the stove over medium-low heat until hot and simmering. Taste and adjust seasoning as needed. Avoid boiling hard so you keep the flavors balanced.

Make cheesy toast fresh just before serving for best results. If you need to prep ahead, toast plain bread and keep it at room temperature for a few hours, then add cheese and grill right before serving. Don’t freeze cheesy toast with the bread and cheese assembled — it’ll get soggy.

Caramelized onions can be made ahead and stored in the fridge for up to 5 days or frozen for a few months. Reheat gently in a pan before making the soup.

Frequently Asked Questions

• Can I make this vegetarian? Yes! Just swap beef broth for a rich vegetable stock and choose a vegetarian melting cheese to keep big flavor without meat.
• Is wine necessary? No — it adds flavor and helps deglaze the pot, but you can skip it and use a splash of broth instead.
• What’s the best cheese to use? Gruyère is the classic choice thanks to its nutty taste and great melting. Mozzarella, Emmental, or other melting cheeses work well too.
• How long does caramelizing onions take? Plan for about 45–60 minutes on the stove for a large batch. The slow cooker method is roughly 10 hours on LOW plus 10–15 minutes finishing on the stove.
• Do I need oven-proof bowls? Not necessarily. While broiling in oven-safe bowls looks gorgeous, it’s perfectly fine — and often better — to grill the cheesy toast separately and add it just before serving so it stays crisp.
• How many servings does the recipe make? The recipe card says 4 servings. (Note, nutrition info assumes 6 servings.)
• Which broth is best? A good quality beef stock is ideal for authentic flavor. If you can’t find a decent beef broth, use chicken or vegetable stock instead — better quality chicken or veggie broth beats poor beef stock any day.

• Can I make the soup ahead? Absolutely. Prepare the soup (without bread), chill it, then reheat and top with fresh grilled cheesy toast when ready to eat.