Croque Monsieur Breakfast Casserole with Ham and Gruyere

Perfect for a holiday brunch or a relaxed long weekend morning, this Croque Monsieur Breakfast Casserole comes together easily and delivers rich, savory flavor that pleases a crowd. It captures all the comforting elements of the classic French sandwich—ham, Gruyère, Dijon, and thyme—transformed into a hands-off, oven-baked brunch centerpiece with crisp edges, a tender custard center, and bubbly, golden cheese.

This casserole is particularly convenient because it uses day-old croissants, which soak up the egg custard in a way that makes the finished dish rich without becoming soggy—think savory bread pudding. The recipe pairs chopped Black Forest ham with shredded Gruyère and a sprinkle of Parmesan, then brightens the flavor with Dijon mustard and fresh thyme. It’s ideal for serving family and friends: you can assemble it ahead of time, bake when guests arrive, and let the kitchen fill with warm, irresistible aromas.

Ingredients

• 4 tablespoons unsalted butter, melted and cooled, plus more for greasing
• 5 cups torn day-old croissant pieces (about 3–4 large croissants)
• 1/2 pound thinly sliced Black Forest ham, roughly chopped
• 1½ cups shredded Gruyère cheese, divided
• 8 large eggs
• 1½ cups whole milk
• 1/2 cup whole milk Greek yogurt
• 1 teaspoon kosher salt
• 1 teaspoon freshly ground black pepper
• 1 teaspoon garlic powder
• 1 tablespoon Dijon mustard
• 1 tablespoon roughly chopped fresh thyme leaves, plus extra for garnish
• 1/2 cup grated Parmesan cheese

Step-by-Step Instructions

Step One: Preheat and prepare

Place one oven rack in the middle and a second rack near the top. Preheat the oven to 375°F (190°C). Butter a 9×13-inch baking dish so the casserole won’t stick.

Step Two: Layer croissants, ham, and cheese

Arrange the torn croissant pieces in an even layer in the prepared dish. Scatter the chopped ham over the croissants and sprinkle 1 cup of the shredded Gruyère evenly across the top.

Step Three: Whisk the custard

In a medium bowl, whisk together the melted butter, eggs, whole milk, Greek yogurt, kosher salt, black pepper, garlic powder, Dijon mustard, and fresh thyme until smooth and well combined.

Step Four: Combine and top

Carefully pour the egg mixture over the croissant, ham, and cheese, pressing gently so the croissant pieces begin to absorb the custard evenly. Sprinkle the remaining 1/2 cup Gruyère and the grated Parmesan over the top.

Step Five: Bake

Bake on the middle rack for 30 minutes. Then move the casserole to the higher rack and bake an additional 15–20 minutes, or until the top is a deep golden brown and the center is set. Total bake time is about 45–50 minutes.

Step Six: Rest and serve

Let the casserole rest for 10–15 minutes to firm up, then garnish with a few extra thyme leaves. Cut into 8 squares and serve warm. The casserole pairs beautifully with a light green salad, roasted tomatoes, or fruit for a balanced brunch spread.

Recipe Details

Prep: 15 minutes · Cook: 50 minutes · Total: 1 hour 5 minutes · Servings: 8

Tips, Variations, and Storage

– If you only have fresh croissants, dry them out by leaving them uncovered on the counter overnight or bake the whole croissants at 375°F for about 10 minutes until they’re slightly dry to the touch. Day-old croissants are preferred because they absorb the custard without becoming mushy.

– This casserole is an excellent way to use leftover holiday ham: substitute 1–2 cups of diced cooked ham if that’s what you have on hand.

– Make-ahead: Assemble the casserole, cover, and refrigerate overnight. Add a few extra minutes to the baking time if baking directly from cold.

– Leftovers keep refrigerated for 3–4 days. Reheat individual portions in a 350°F oven until warmed through, or use a microwave for a quick single serving (cover to retain moisture).

Frequently Asked Questions

Nutrition (approximate per recipe)

Calories: 950 kcal · Carbohydrates: 72 g · Protein: 36 g · Fat: 57 g · Saturated Fat: 30 g · Sodium: 1,587 mg · Fiber: 4 g · Sugar: 20 g

Nutrition information is automatically calculated and should be used as an approximation.

Want more brunch-friendly recipes? Try these ideas

Mini Ham and Gruyère Quiches • Sausage McMuffin Egg Bake • Broccoli Cheddar Egg Bites • Italian Sausage and Arugula Quiche • Old Fashioned Breakfast Casserole

Photography and styling by Eat Love Eats.

If you make this Croque Monsieur Breakfast Casserole, leave a comment and let us know how it turned out — any small tweaks or serving ideas are always welcome!