Mushroom and Gruyère Croissant Breakfast Casserole Recipe

This elegant Mushroom and Gruyère Croissant Breakfast Casserole Recipe layers buttery, mustard-brushed pastries with an earthy ragout of wild mushrooms and a velvety Dijon custard. Baked until the croissants are golden-crisp on top and meltingly soft underneath, it offers a sophisticated, savory bread pudding texture. It is the ultimate make-ahead centerpiece for a luxurious holiday brunch or a slow Sunday morning for the whole family.

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Mushroom and Gruyère Croissant Casserole Ingredients

The Savory Filling:

• 1 pound mixed wild mushrooms: Finely chopped. Cremini, shiitake, or oyster mushrooms provide a deep, meaty umami flavor.
• Aromatics: 1 large shallot (sliced) and 2 garlic cloves (minced) for a sweet, pungent base.
• 2 tablespoons fresh thyme: The woodsy herb that pairs perfectly with mushrooms.
• 1 tablespoon sherry vinegar: A splash of acid to deglaze the pan and brighten the earthiness.
• 4 ounces cream cheese: Softened, to bind the filling.
• 2 scallions: Thinly sliced.

The Structure:

• 10 small plain croissants: Sliced in half. Stale croissants work best as they absorb the liquid without disintegrating.
• 8 ounces Gruyère cheese: Shredded. Divided between the filling and the topping for that signature Swiss nuttiness and melt.
• 1 tablespoon + 5 teaspoons Dijon mustard: Used to brush the croissants and flavor the custard.

The Custard:

• 10 large eggs: The foundation of the bake.
• 1 1/4 cups half-and-half: Provides richness.
• 4 tablespoons unsalted butter: For sautéing.
• Kosher salt & Black pepper: To taste.

How To Make Mushroom and Gruyère Croissant Casserole

1. Sauté the Mushrooms: Melt the butter in a large skillet over medium heat. Add the chopped mushrooms, garlic, shallots, thyme, salt, and pepper. Cook, stirring frequently, for about 5 minutes until the mushrooms release their liquid, it evaporates, and they begin to brown. Stir in the sherry vinegar to scrape up the flavorful browned bits (fond) from the bottom.
2. Enrich the Mixture: Transfer the hot mushroom mixture to a large bowl and let it cool for 5 minutes. Stir in the softened cream cheese, 1 cup of the shredded Gruyère, and half of the scallions until you have a thick, creamy mushroom paste.
3. Whisk the Custard: In a separate bowl, whisk together the eggs, half-and-half, 1 tablespoon of Dijon mustard, the remaining scallions, salt, and pepper until completely smooth.
4. Prep the Croissants: Lightly grease a 9×13-inch baking dish. Slice the croissants in half lengthwise. Spread 1/2 teaspoon of Dijon mustard onto the interior cut sides of every croissant piece (top and bottom).
5. Stuff and Arrange: Place the croissant bottoms in the baking dish. Spoon the mushroom-cheese mixture generously over the bottoms, then cap them with the croissant tops. It’s okay if the filling spills over; rustic is good.
6. Soak: Pour the egg custard evenly over and around the stuffed croissants. Sprinkle the remaining 1 cup of Gruyère cheese over the top. Cover tightly and refrigerate for at least 4 hours, or ideally overnight. This allows the pastry to drink up the custard.
7. Bake: Preheat oven to 350°F. Bake the casserole covered with foil for 30 minutes until puffed. Remove the foil and bake for another 15 minutes until the custard is set and the croissant tops are deep golden brown and crispy. Let stand for 5 minutes before serving.

Recipe Tips

• The Soak is Non-Negotiable: Because croissants are flaky and fatty, they take time to absorb the egg mixture. If you bake it immediately, you’ll have dry bread floating in scrambled eggs. Give it the full overnight rest.
• Cleaning Mushrooms: Do not soak mushrooms in water; they act like sponges. Wipe them clean with a damp paper towel or use a soft mushroom brush to remove dirt.
• Mustard Matters: The Dijon adds a sharp, vinegary punch that cuts through the intense richness of the cream cheese, butter, and croissant dough. Don’t skip the brushing step!
• Sherry Substitute: If you don’t have sherry vinegar, a splash of dry white wine or apple cider vinegar works well to deglaze the pan.

What To Serve With Breakfast Casserole

• Arugula Salad: A peppery green salad with a lemon vinaigrette is essential to balance the heaviness of the dish.
• Fruit Salad: Citrus segments (grapefruit and orange) provide a refreshing palate cleanser.
• Crispy Bacon: If you need meat, serve bacon or sausage links on the side.
• Mimosas: The bubbles and acid cut through the dairy richness.

How To Store Mushroom Croissant Casserole

• Refrigerate: Store baked leftovers covered in the fridge for up to 3 days.
• Reheat: Cover with foil and warm in a 350°F oven for 20 minutes. Microwaving tends to make the croissants chewy and soggy.
• Freeze: You can freeze the baked casserole. Wrap individual slices in plastic and foil. Thaw in the fridge before reheating.

Mushroom and Gruyère Casserole Nutrition Facts

• Calories: 580 kcal
• Fat: 38g
• Carbohydrates: 32g
• Protein: 24g
• Cholesterol: 290mg

Nutrition information is estimated per serving.

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