Hey there, friends! There’s something about stepping into your kitchen on a cool evening and smelling that sweet, caramelized onion aroma drifting through the air. It’s like a warm hug that starts at your nose and works its way down to your toes. You know the kind of comfort I’m talking about—cozy, homey, and a little bit indulgent.
Imagine that same deep onion flavor and rich broth you love in French onion soup, but reimagined as a layered casserole that you can slice and serve without wrestling with ladles. Trust me, this twist has been on heavy rotation in my house lately—and once you try it, you’ll understand why.
Why You’ll Love It
This casserole brings all the cozy vibes of French onion soup—jammy onions, fragrant thyme, a splash of wine—without the fuss of ladling. Instead, you get neat squares of toasted bread soaking up that savory goodness, crowned with gooey cheese that bubbles and browns in the oven. It’s perfect for unwinding with a glass of your go-to white—something crisp, like a Chardonnay or Sauvignon Blanc (I’m partial to a California bottle these days). Plus, it’s a crowd-pleaser: send out a platter, hear the “oohs” and “aahs,” and watch everyone dive in.
Timing and Servings
• Prep: about 15 minutes
• Caramelizing onions: 15 minutes
• Bake time: 20–25 minutes
Total, just under an hour. It makes enough to feed six hungry folks or a smaller group if plates keep coming back for seconds. If you’ve ever stared at a half-empty pot of soup wishing for leftovers that felt fresh, this casserole’s your new best friend.
Ingredients
• 3 tablespoons unsalted butter
• 3 large sweet onions, thinly sliced
• 2 cloves garlic, minced
• Salt and pepper, to taste
• 1 teaspoon fresh or dried thyme
• 2 tablespoons all-purpose flour
• ½ cup dry white wine
• 2 cups beef broth
• 1 cup chicken broth
• 6 slices day-old French bread or baguette, toasted
• 1½ cups grated Gruyère cheese
• ½ cup grated Parmesan cheese
• Fresh parsley, chopped (for garnish)
• Cooking spray
Feel free to swap out broths or cheeses—there’s a section below all about that.
Directions
- Preheat your oven to 400°F (200°C). Grease a 9×13-inch baking dish with cooking spray.
- In a large skillet over medium heat, melt the butter. Add the onions, stirring every few minutes until they’re golden and jam-like. Give yourself a small reward halfway—maybe a sip of that wine.
- Stir in garlic, thyme, salt, and pepper. After about a minute, sprinkle on the flour and stir for 2 minutes, so you don’t get any floury taste.
- Pour in the wine slowly; it’ll bubble like crazy. Let it reduce by half—around 2–3 minutes—then add both broths. Simmer for 8–10 minutes until it thickens slightly. If you’re multitasking, start warming that wine glass again.
- Spoon half the onion mixture into the baking dish. Layer three toasted bread slices on top, then sprinkle half the cheeses. Repeat with the remaining onions, bread, and cheeses.
- Bake uncovered for 20–25 minutes until the cheese is melted, bubbly, and golden at the edges.
- Let it rest for 5 minutes so everything sets up nicely. Sprinkle parsley on top and serve straight from the dish.
Variations
Want to shake things up? Swap beef broth for vegetable broth to lighten things up, or add a handful of sliced mushrooms when you’re cooking the onions—those fungi soak up flavor like nobody’s business. Dairy-free? There are plant-based cheeses that crisp nicely, so you won’t miss out. Gluten-free? Grab your favorite loaf, toast it, and treat it just like the French bread.
Feeling bold? Try a sprinkle of smoked paprika or a dash of hot sauce in the onion mixture. You’ll taste a subtle kick that makes each bite even more memorable.
Storage & Reheating Tips
Leftovers are almost better than the first go-round. Store any extras in an airtight container in the fridge for up to 3 days. To reheat:
• Oven: 350°F for 10–12 minutes until warmed through
• Microwave: 1–2 minutes on medium power, stirring halfway
If you want to stash a whole casserole for later, wrap it tightly in foil and freeze for up to two months. Thaw it in the fridge overnight and bake as directed—add a few extra minutes if it’s still chilled.
FAQs
Can I use a different cheese?
Absolutely. Sharp cheddar gives a tangy edge, mozzarella brings that stretchy pull, and Swiss or Emmental add nuttiness. Mix and match until you find your dream combo.
What if I don’t have wine?
No problem. Swap the wine for an extra ½ cup broth plus a teaspoon of vinegar (red or white). It adds brightness without missing a beat.
Is day-old bread really necessary?
Best results come from slightly stale bread that soaks but stays intact. If fresh is all you’ve got, toast it a bit longer so it holds up under the sauce.
Can I make it ahead?
Sure thing. Assemble everything, cover, and refrigerate for up to 24 hours. When you bake it, just tack on a few more minutes so it heats all the way through.
Conclusion
This French onion soup casserole is proof that you can take a classic, nudge it into a new shape, and still feel that familiar warmth. It’s simple enough for busy weeknights, yet special enough for gatherings—whether it’s a Sunday supper or a last-minute drop-in. Give it a try, pour yourself a glass of wine, and revel in the comforting layers of onions, bread, and cheese. Before you know it, this cozy dish will be your new go-to—and you’ll wonder how you ever lived without it.
French Onion Soup Casserole
Ingredients
- 3 tbsp unsalted butter
- 3 large sweet onions thinly sliced
- 2 cloves garlic minced
- Salt and pepper to taste
- 1 tsp thyme fresh or dried
- 2 tbsp all-purpose flour
- 1/2 cup dry white wine
- 2 cups beef broth
- 1 cup chicken broth
- 6 slices day-old French bread or baguette toasted
- 1 1/2 cups grated Gruyère cheese
- 1/2 cup grated Parmesan cheese
- 1/4 cup fresh parsley chopped (for garnish)
- Cooking spray
Instructions
- Preheat oven to 400°F (200°C). Spray a 9x13 inch baking dish with cooking spray.
- Melt butter in a large pan over medium heat. Add onions and cook, stirring occasionally, until soft and golden brown, about 15 minutes. Add garlic, salt, pepper, and thyme; cook for 1 minute.
- Stir in flour and cook for 2 minutes. Pour in the wine and simmer until reduced slightly. Add beef and chicken broths; simmer for 10 minutes.
- Pour half of the onion mixture into the prepared dish. Layer half of the toasted bread on top, then sprinkle with half of both cheeses. Repeat layers with remaining ingredients.
- Bake uncovered for 20-25 minutes, or until cheese is bubbly and golden.
- Let it sit for a few minutes to set. Garnish with fresh parsley before serving.
Notes
- Swap beef broth with chicken or veggie broth for a different flavor.
- Experiment with cheeses like sharp cheddar or mozzarella.
- Use gluten-free bread for a gluten-free option.
- Prep ahead and bake when ready. For a time-saver, use store-bought caramelized onions.
