Overnight Croque Monsieur Casserole Recipe
This Overnight Croque Monsieur Casserole elevates the classic French sandwich into a hearty, make-ahead breakfast or brunch dish. Featuring layers of buttery bread, caramelized onions, garlic, Canadian bacon, Gruyere, and a creamy mustard-egg custard, it bakes to a golden, cheesy perfection. With a simple overnight soak, it’s perfect for busy mornings or entertaining guests.
- Prep Time: 20 minutes
- Cook Time: 50 minutes
- Total Time: 3 hours 20 minutes to 12 hours 20 minutes (including overnight soak)
- Yield: 12 servings 1x
- Category: Breakfast Casserole
- Method: Baking
- Cuisine: French-American
Ingredients
Scale
Bread and Butter
- 1 Loaf Martin’s Old-Fashioned Real Butter Bread, stale or toasted, cut into thick cubes
- Unsalted Butter, plus more to coat pan (about 1 tablespoon plus extra for greasing)
Vegetables and Herbs
- 1 Yellow Onion, roughly chopped (about 1 1/2 cups)
- 4 Cloves Garlic, thinly sliced
- 1 Tablespoon Fresh Thyme, roughly chopped, plus 1 teaspoon for garnish
- Salt and Pepper, to taste
Dairy and Eggs
- 8 Large Eggs
- 1 1/2 Cups Half-and-Half
- 2 Cups Gruyere Cheese, shredded (about 4.5 ounces)
- 1/4 Cup Parmesan Cheese, finely grated (about 1 ounce)
Meat
- 1/2 Pound Canadian Bacon, cut into 1/2-inch dice
Other
- 2 Tablespoons Dijon Mustard
- 1/2 Teaspoon Hot Sauce, plus more for garnish
- 1 1/2 Teaspoons Kosher Salt
Instructions
- Prepare the Baking Dish: Coat a 3-quart (13×9-inch) baking dish generously with butter to prevent sticking and set it aside for later use.
- Sauté Onions and Garlic: Heat a large frying pan over medium heat and add 1 tablespoon unsalted butter. When the butter is slightly frothy, add the roughly chopped onion and season with salt. Cook until the onions are just softened, about 3 to 4 minutes. Add the thinly sliced garlic, season with salt and pepper, and cook for another minute until fragrant. Remove from heat and stir in the fresh thyme.
- Mix the Custard: In a large bowl, whisk together the eggs, half-and-half, Dijon mustard, hot sauce, and kosher salt until the mixture is smooth and uniform.
- Layer the Casserole: Arrange half of the cubed butter bread evenly in the bottom of the prepared baking dish. Sprinkle with 1 cup of shredded Gruyere cheese and half of the sautéed onion-garlic mixture and diced Canadian bacon. Repeat the layers with the remaining bread, onion mixture, Canadian bacon, and Gruyere cheese. Pour the egg custard evenly over the top.
- Soak Overnight: Press down on the bread gently to fully submerge it in the egg custard. Cover the dish tightly with plastic wrap and place a heavy plate on top to weigh it down. Refrigerate the casserole for 3 to 12 hours to allow the bread to absorb the custard.
- Bake Covered: When ready to bake, remove the plastic wrap and weight. Cover the casserole with aluminum foil and place it on the middle rack of the oven. Set the oven temperature to 325°F (no need to preheat) and bake for 35 minutes.
- Bake Uncovered and Finish: Remove the foil, sprinkle the finely grated Parmesan cheese over the casserole, then increase the oven temperature to 375°F. Bake for an additional 10 to 15 minutes until the top is golden brown and bubbly.
- Garnish and Serve: Remove the casserole from the oven and sprinkle the remaining fresh thyme on top. Let it cool for at least 5 minutes before serving. Offer additional hot sauce on the side for those who enjoy a spicy kick.
Notes
- Use stale or toasted bread to ensure it soaks up the custard well without becoming too soggy.
- Letting the casserole soak overnight improves flavor and texture, but a minimum of 3 hours will work in a pinch.
- Gruyere cheese provides classic nutty flavor; substitutions like Emmental or Jarlsberg can be used if unavailable.
- Adjust hot sauce to your heat preference or omit for a milder dish.
- You can prepare the casserole entirely in advance and refrigerate before baking for convenience.
Keywords: Croque Monsieur, breakfast casserole, make-ahead brunch, French breakfast, egg custard bake, Gruyere cheese, Canadian bacon
