Buttery croissants are paired with salty feta, savory mushrooms, and eggs in this easy Croissant Breakfast Casserole! This is a fantastic vegetarian breakfast casserole to serve to a crowd.
On a recent trip to Costco I picked up a 12 pack of croissants with no plan, and was left wondering what in the world to do with them. Since I grew up on breakfast casseroles, I figured I could swap my classic hash browns for cubed croissants.
The result is fantastic. Buttery croissant pieces crisp up even more in the oven and create an almost quiche-like egg casserole when paired with mushrooms, spinach, and feta.
This is sure to be a new classic in my Christmas day casserole rotation, but it would also be great for Mother's Day and Easter!
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Recipe overview
- Makes 4-5 servings, depending on your appetite. While it's meant for breakfast and brunch, I've eaten leftovers for dinner more than once.
- This breakfast casserole is vegetarian as-is, but you can sauté up extra protein and add it alongside the mushrooms and spinach.
- The croissant pieces become extra crispy and golden after baking. It's like a croissant breakfast sandwich but in casserole form!
Ingredients
- Croissants: Just three large croissants is all you need. Cut them into 1-inch pieces.
- Eggs: Choose large eggs.
- Feta: I love the saltiness that feta adds, but this casserole all works with gruyere, Parmesan, or asiago cheese.
- Milk: 2% is my go-to for eggs, but I've also had success with unsweetened soy milk and whole milk.
- Spinach and mushrooms: I use cremini mushrooms and fresh spinach. Frozen spinach works, but should be cooked before adding to the eggs.
Step-by-step instructions
- Heat a large skillet over medium heat. Drizzle with olive oil. Once hot, add the diced mushrooms. Cook until golden, about 6-8 minutes, then stir in the spinach, garlic, and salt. Continue cooking until the spinach is wilted and garlic is golden. Remove from the heat.
- While the mushrooms cook, whisk together the egg filling until well combined: eggs, milk, salt, pepper, and optional red pepper flakes.
- Assemble the casserole in a greased 9x9-inch or similarly sized baking dish, such as 8x11 or 10x10. Cut the croissants into 1-inch cubes, then layer on the bottom. Top with the vegetables, then sprinkle with feta. Pour the egg mixture across the top of the veggies. The croissant pieces should be mostly covered, but its okay if some edges poke out.
- Bake at 350F for 30 minutes, or until the eggs are set in the center and pulling away from the edges of the pan. Serve & enjoy!
Cassidy's tips
- If the croissants are browned but the eggs aren't cooked through, tent the baking dish with foil.
- I have not tried doubling this recipe. If you would like to try it, my recommendation is to bake the egg casserole in a 9x13-inch baking dish. It will likely need extra cooking time, so check it at 30 minutes but add additional time as needed.
Storage notes
- Leftover pieces of egg casserole keep well for 3-4 days. Keep refrigerated.
- Individual slices reheat well in the microwave, and the entire casserole can be reheated in the oven at 325F in 20-25 minutes. Cover tightly with foil to avoid overcooking the casserole while reheating.
- Freeze the casserole in individual slices or as an an entire casserole. Cover with plastic wrap and foil, then freeze for up to 3 months. Let thaw in the fridge overnight before reheating.
- I don't recommend prepping the casserole ahead, as the croissants will soften too much. Instead, assemble everything except for the eggs in the casserole dish. Keep the egg mixture separate, pouring into the dish just before baking.
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Croissant Egg Casserole with Mushrooms & Spinach
This vegetarian breakfast egg casserole features sautéed spinach and mushrooms, buttery croissant pieces, and feta cheese.
Ingredients
- 3 large croissants
- 2-3 teaspoons olive oil
- 8 ounces baby bella mushrooms roughly chopped
- ½ medium white onion diced
- 3 handfuls spinach roughly 3 cups
- 3 cloves garlic minced
- 1 teaspoon kosher salt divided
- 8 large eggs
- ½ cup milk 2%, whole, unsweetened soy all work
- ½ teaspoon red pepper flakes optional
- ¼ teaspoon black pepper
- 1 cup crumbled feta
Instructions
- Preheat the oven to 350F. Cut or tear the croissants into 1-inch pieces. Set aside.
- Heat a large skillet over medium heat. Drizzle with olive oil. Once hot, add the chopped mushrooms and diced onion. Cook until golden, about 6-8 minutes, then stir in the spinach, garlic, and ½ teaspoon of the salt. Continue cooking until the spinach is wilted and the garlic is golden. Remove from the heat.
- While the mushrooms cook, whisk together the egg filling in a bowl until well combined: eggs, milk, remaining ½ teaspoon salt, optional red pepper flakes, and black pepper.
- Grease a 9x9-inch or similarly sized baking dish, such as 8x11 or 10x10. Layer the cubed croissant pieces across the bottom of the dish. Top with the sautéed ingredients, then sprinkle with feta. Pour the egg mixture across the top of the veggies. The croissant pieces should be mostly covered, but its okay if some edges poke out.
- Bake at 350F for 30 minutes, or until the eggs are completely set in the center and the edges are pulling away from the pan. If the croissants brown too quickly, loosely tent with a sheet of foil. Serve & enjoy!
Video
Notes
- How to freeze: Freeze the casserole in individual slices or as an an entire casserole. Cover with plastic wrap and foil, then freeze for up to 3 months. Let thaw in the fridge overnight before reheating.
- To prep in advance: I don't recommend assembling the casserole ahead, as the croissants will soften too much. Instead, assemble everything except for the eggs in the casserole dish. Keep the egg mixture separate, pouring into the dish just before baking.
- If the croissants are browned but the eggs aren't cooked through, tent the baking dish with foil.
Nutrition
Calories: 509kcalCarbohydrates: 32gProtein: 25gFat: 31gSaturated Fat: 15gPolyunsaturated Fat: 3gMonounsaturated Fat: 10gTrans Fat: 0.04gCholesterol: 443mgSodium: 1378mgPotassium: 677mgFiber: 2gSugar: 9gVitamin A: 3233IUVitamin C: 8mgCalcium: 338mgIron: 4mg
Did you make this?I love hearing how it went! Leave a review or tag me on Instagram @cozypeachkitchen so I can see your creations!
David says
I love all of the instructions- very detailed! Thanks
Sadie says
Do I use already baked croissants or like dough from the package
Cassidy Reeser, MS, RD says
Hi Sadie, I think I replied to your email yesterday but in case others have the same question: use baked croissants like from a bakery. I get them from Costco or Whole Foods.