Make Ahead Spinach and Mushroom Egg Casserole

Make Ahead Spinach and Mushroom Egg Casserole is a healthy, make-ahead breakfast casserole that’s perfect for holidays, brunches, and busy mornings. This cheesy spinach mushroom egg bake is loaded with vegetables, packed with protein, and baked until perfectly fluffy and comforting.

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Best of all, it can be prepped ahead of time, making it ideal for Mother’s Day brunch, Easter morning, or any stress-free family gathering where you want an easy breakfast casserole ready to go in the oven.

This spinach mushroom egg bake is a vegetarian breakfast casserole that feels special enough for guests but easy enough for everyday meal prep. Whether you call it a mushroom breakfast casserole, egg spinach casserole, or a cheesy mushroom spinach egg casserole, it’s one recipe you’ll want to keep in rotation.

Why You’ll Love This Spinach and Mushroom Egg Casserole

• This healthy spinach egg casserole is simple, satisfying, and incredibly versatile
• Perfect make-ahead breakfast casserole with spinach
• Vegetarian-friendly and packed with nutrients
• Great for brunch, holidays, or even spinach egg casserole for dinner
• Customizable with different cheeses or add-ins
• Reheats beautifully for meal prep
• The kind of spinach mushroom breakfast casserole that works just as well for a cozy weekend morning as it does for feeding a crowd

Ingredients Needed for This Easy Spinach Egg Casserole

This recipe uses simple, wholesome ingredients you can find at any grocery store. They come together to create a cheesy spinach and egg casserole that’s rich without being heavy.

• 1 tablespoon Olive Oil
• ½ large Onion, chopped
• 1 Red Bell Pepper, chopped
• 2 (8 oz) packages Fresh Mushrooms, sliced (about 4 cups)
• ¼ teaspoon Salt
• ¼ teaspoon Black Pepper
• ¼ teaspoon Garlic Powder
• 4 cups Fresh Baby Spinach
• 10 large Eggs
• ¾ cup Whole Milk or Half and Half
• 8 oz Swiss Cheese, shredded (about 3–4 cups)

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Tools Needed

You don’t need anything fancy to make this egg bake casserole, which is another reason it’s so stress-free.

• Large sauté pan or skillet
• Cutting board and knife
• Mixing bowl
• Whisk
• Cheese grater
• 13×9-inch baking dish
• Measuring cups and spoons

How To Make Easy Spinach and Mushroom Egg Bake

This step-by-step method makes it easy to see how to make spinach and mushroom egg bake without overthinking it.

1. Preheat your oven to 350°F and lightly grease a 13×9 baking dish.
2. Heat olive oil in a large skillet over medium heat.
3. Sauté the chopped onion and red bell pepper for about 2 minutes, until slightly softened.
4. Add sliced mushrooms, salt, pepper, and garlic powder. Cook for 2–4 minutes, until mushrooms release their moisture.
5. Add spinach and cook just until wilted. Remove from heat.
6. In a large bowl, whisk together the eggs and milk (or half and half).
7. Stir in the shredded Swiss cheese.
8. Fold the sautéed vegetables into the egg mixture.
9. Pour everything into the prepared baking dish.
10. Bake for 40 minutes, or until the center is set and the top is lightly golden.
11. Let the casserole rest for 5–10 minutes before slicing.

My Story: Why This Make-Ahead Breakfast Casserole Is a Holiday Lifesaver

I started making egg spinach casserole recipes years ago when holiday mornings felt more chaotic than joyful. Between hosting family, getting kids dressed, last minute clean up, and trying to enjoy special moments, cooking a full breakfast always added unnecessary stress.

That’s when I discovered the magic of make-ahead spinach mushroom egg casserole. I was at a relative’s home for Thanksgiving, where Cousion Pete showed me how to make his Easy Sausage and Cheese Overnight Breakfast Casserole. We love this recipe, but I also wanted to make a vegetarian version.

I prep everything the night before, cover it, and store it in the fridge. On Easter morning or Mother’s Day brunch, all I have to do is slide it into the oven. At Thanksgiving, I make 2 of these recipes and have them ready for the long family weekend.

Instead of juggling pans and timing, I can sit with my coffee, enjoy conversations, and actually be present. This healthy breakfast casserole has truly changed how I approach family holidays. Less stress, more connection, and still a delicious homemade meal everyone loves.

Casserole Variations

• Cheesy Mushroom Spinach Egg Casserole: Swap Swiss cheese for cheddar, mozzarella, Gruyère, or pepper jack for a different flavor profile.
• Spinach Mushroom Cottage Cheese Egg Bake: Replace half of the shredded cheese with cottage cheese for extra protein and a creamier texture.
• Mushroom Breakfast Casserole with Extra Veggies: Add diced zucchini, broccoli florets, asparagus, or tomatoes to boost the vegetable content even more.
• Spinach and Egg Casserole with Protein: For non-vegetarians, stir in cooked breakfast sausage, bacon, or ham to turn it into a heartier breakfast or dinner option.
• Healthy Spinach Egg Casserole: Use low-fat milk, reduce the cheese slightly, and add extra spinach for a lighter version that’s still satisfying.
• Egg Cheese Spinach Breakfast Casserole for Dinner: Season with a pinch of red pepper flakes or Italian seasoning to make it feel more savory and dinner-ready.

Frequently Asked Questions (FAQs)

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