Mushroom and Gruyère Croissant Breakfast Casserole
This vegetarian breakfast casserole is easy to assemble up to a day ahead and bake off in the morning, making it the perfect addition to your brunch menu. Meaty mushrooms stand in for the typical breakfast proteins and dish is rounded out with a generous amount of creamy Gruyère, plus fresh thyme and tangy Dijon mustard. We use buttery, flaky croissants as the perfect vessel to sandwich the cheesy mushroom filling and soak up all the custardy eggs.
Ingredients
Method
- Melt the butter in a large skillet over medium heat. Add the mushrooms, garlic, shallots, thyme, 1 teaspoon salt and several grinds of black pepper. Cook, stirring frequently, until the mushrooms are tender and browned in spots, about 5 minutes. Stir in the sherry vinegar and scrape up any brown bits from the bottom of the skillet. Transfer to a large bowl to cool slightly, 5 minutes.
- Stir the cream cheese, half of the Gruyère and half of the sliced scallions into the mushroom mixture.
- Whisk together the eggs, single cream, 1 tablespoon of the Dijon, remaining scallions, 3/4 teaspoon salt and several grinds of black pepper in another large bowl until very smooth; set aside.
- Lightly grease a 9-by-13-inch baking dish with butter. Cut the croissants in half lengthwise. Spread 1/2 teaspoon of Dijon on the inside of each croissant, top and bottom. Arrange the bottom halves of the croissants in the prepared baking dish. Divide the mushroom mixture between the croissant bottoms and then sandwich with the top halves; the croissants will be filled generously and it’s ok if a few of the mushrooms spill over into the baking dish.
- Pour the egg mixture over and around the croissants. Sprinkle the top of the croissants with the remaining Gruyère. Cover and refrigerate for at least 4 hours or preferably overnight.
- When ready to bake, preheat the oven to 180 degrees C.
- Cover the baking dish with foil and bake until the egg has puffed and nearly set, about 30 minutes. Uncover and bake until the eggs are completely set and the croissants are golden, about 15 minutes more. Let sit for 5 minutes before serving.
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