French Onion Casserole

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Warm, comforting, and irresistibly cheesy—French Onion Casserole takes everything you love about classic French onion soup and turns it into a hearty, baked dish. With golden caramelized onions, savory broth, crusty bread, and melty Gruyère cheese, every bite delivers cozy satisfaction with a gourmet twist. This is the kind of meal that turns a chilly evening into a warm memory.

Whether you’re looking for a cozy weeknight dinner, a standout potluck option, or an indulgent comfort food fix, this casserole hits the spot. It’s rich, savory, and deeply flavorful, with that signature stretch of cheese that’s bound to make mouths water.

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Ingredients for this French Onion Casserole

• 4 large yellow onions, thinly sliced
• 3 tablespoons unsalted butter
• 1 tablespoon olive oil
• 2 teaspoons sugar
• 1 teaspoon salt
• 1/2 teaspoon black pepper
• 1 teaspoon fresh thyme leaves (or 1/2 tsp dried thyme)
• 2 cloves garlic, minced
• 1/2 cup dry white wine (optional)
• 2 cups beef broth
• 1 tablespoon Worcestershire sauce
• 6 thick slices of crusty French bread (day-old is best)
• 2 cups shredded Gruyère cheese
• 1 cup shredded mozzarella cheese
• 1/4 cup grated Parmesan cheese

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Step 1: Caramelize the Onions

In a large skillet over medium heat, melt the butter and olive oil together. Add the sliced onions, sugar, salt, and pepper. Cook slowly, stirring occasionally, for about 25–30 minutes until the onions are soft, golden brown, and deeply caramelized. This step builds the deep, sweet flavor base of the casserole—don’t rush it!

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Step 2: Add Garlic, Herbs & Deglaze

Once the onions are beautifully caramelized, stir in the minced garlic and thyme. Sauté for another minute until fragrant. If using, pour in the white wine to deglaze the pan, scraping up any browned bits. Simmer for 2–3 minutes until the wine is mostly evaporated.

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Step 3: Build the Broth Base

Stir in the beef broth and Worcestershire sauce. Let everything simmer together for 5–7 minutes so the flavors meld. Then remove from heat.

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Step 4: Toast the Bread

While the onion mixture is simmering, preheat your oven to 375°F (190°C). Lay the bread slices on a baking sheet and toast them in the oven for about 5 minutes per side, until crisp and golden. This helps the bread hold up in the casserole and adds a lovely texture.

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Step 5: Assemble the Casserole

In a greased 9×9 baking dish or similar casserole dish, layer half of the toasted bread slices at the bottom. Spoon over half the onion mixture, then sprinkle with half the cheeses (Gruyère, mozzarella, and a little Parmesan). Repeat with the remaining bread, onions, and cheeses.

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Step 6: Bake Until Golden & Bubbling

Cover with foil and bake for 20 minutes. Then uncover and bake for another 10–15 minutes, or until the cheese is melted, bubbly, and golden brown on top. If desired, broil for 2 minutes to get an extra-toasty cheese crust.

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Step 7: Garnish & Serve

Let the casserole cool slightly before serving. Top with fresh thyme or chopped parsley for a pop of color and added aroma. Serve warm and enjoy the melty, savory magic.

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Storage Instructions

To store leftover French Onion Casserole, let it cool to room temperature first. Then, cover the dish tightly with foil or transfer portions to an airtight container. It will keep in the refrigerator for up to 4 days.

For longer storage, freeze individual portions wrapped in foil and placed in a freezer-safe container for up to 2 months. When ready to enjoy, reheat in a 350°F (175°C) oven until warmed through—about 20–25 minutes if refrigerated, or 35–40 minutes if frozen.

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Estimated Nutrition (Per Serving – based on 6 servings)

• Calories: 410
• Protein: 18g
• Fat: 25g
• Carbohydrates: 28g
• Fiber: 2g
• Sugar: 6g
• Sodium: 620mg
• Calcium: 320mg

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Frequently Asked Questions

What type of onions work best for this recipe?

Yellow onions are ideal because they caramelize beautifully and have a natural sweetness, but you can also mix in sweet onions for an even richer flavor.

Can I make this casserole vegetarian?

Yes! Simply use vegetable broth instead of beef broth and double-check that your Worcestershire sauce is vegetarian (or use soy sauce as a sub).

What’s the best cheese for French Onion Casserole?

Gruyère is traditional and offers great flavor and meltiness. A combo of Gruyère, mozzarella, and Parmesan creates an irresistible topping.

Do I need to use wine?

Nope! The white wine adds depth, but you can skip it or substitute with a splash of extra broth and a touch of vinegar or lemon juice for acidity.

Can I prepare this dish ahead of time?

Absolutely. Assemble the casserole, cover tightly, and refrigerate for up to 24 hours before baking. Just add 5–10 extra minutes to the bake time if starting cold.

How do I keep the bread from getting soggy?

Toasting the bread is key! It creates a sturdy base that soaks up flavor without turning mushy.

Can I use a different type of bread?

Yes, just make sure it’s thick-cut and crusty. Baguette slices, sourdough, or ciabatta all work well.

What can I serve with French Onion Casserole?

This dish pairs beautifully with a crisp green salad, roasted vegetables, or a simple grilled protein like chicken or steak.

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