Spinach and Mushroom Egg Casserole (Easy & Make-Ahead!)

Start your day right with this incredibly savory and simple Spinach and Mushroom Egg Casserole. This recipe is a powerhouse of flavor and nutrition, packing fluffy eggs, earthy mushrooms, fresh spinach, and melted cheese into one delicious dish. It’s the perfect solution for a stress-free weekday breakfast, a beautiful brunch centerpiece, or even a light and satisfying dinner. If you’re looking for a reliable and crowd-pleasing healthy breakfast casserole, you’ve found it.

This dish isn’t just easy to make; it’s also wonderfully versatile. You can assemble it the night before and pop it in the oven in the morning, making it an ideal choice for busy schedules or holiday gatherings. It reheats beautifully, so you can enjoy a wholesome, protein-packed breakfast all week long.

Why This Spinach and Mushroom Egg Casserole is a Must-Try

• Effortlessly Simple: With just a few common ingredients and straightforward steps, this recipe is accessible to cooks of all skill levels.
• Meal-Prep Friendly: Bake it once and enjoy delicious, ready-to-go breakfasts for days. It’s a fantastic time-saver!
• Nutrient-Packed: Loaded with protein from the eggs and vitamins from the spinach and mushrooms, it’s a breakfast that fuels your body.
• Low-Carb & Keto-Friendly: Naturally low in carbs, this vegetarian breakfast fits perfectly into a keto or low-carb lifestyle without sacrificing flavor. For another great low-carb option, check out this easy low-carb breakfast casserole.

Ingredients for The Perfect Egg Bake

The magic of this Spinach and Mushroom Egg Casserole lies in its simple, high-quality ingredients. Here’s what you’ll need to bring this delicious dish to life.

For the Casserole:

• Large Eggs: The star of the show, providing the fluffy, protein-rich base.
• Fresh Spinach: Provides essential nutrients and a beautiful green color. Be sure to wilt it first to remove excess water.
• Cremini Mushrooms: Sliced and sautéed, they add a deep, savory, umami flavor.
• Onion & Garlic: The aromatic foundation that builds incredible flavor.
• Milk or Heavy Cream: Adds richness and moisture, creating a tender, custardy texture. Use heavy cream for a richer, more decadent result.
• Shredded Cheese: A blend of cheddar and Gruyère provides a sharp, nutty, and perfectly melted topping.
• Olive Oil: For sautéing the vegetables.
• Salt, Black Pepper, and Nutmeg: Simple seasonings that enhance all the other flavors. A pinch of nutmeg is a classic addition that wonderfully complements the spinach and eggs.

Step-by-Step Instructions

Making this make-ahead egg bake is incredibly easy. Follow these simple steps for a perfect casserole every time.

1. Preheat and Prepare: First, preheat your oven to 375°F (190°C). Grease a 9×13 inch baking dish with butter or non-stick spray.
2. Sauté the Vegetables: Heat olive oil in a large skillet over medium heat. Add the chopped onion and cook until softened, about 5 minutes. Add the minced garlic and sliced mushrooms, cooking until the mushrooms have released their moisture and started to brown.
3. Wilt the Spinach: Add the fresh spinach to the skillet in batches. Cook until it has completely wilted down. It’s crucial to cook out as much moisture as possible to prevent a watery casserole. Drain any excess liquid from the pan.
4. Assemble the Base: Spread the cooked spinach and mushroom mixture evenly across the bottom of the prepared baking dish. Sprinkle half of the shredded cheese over the vegetables.
5. Mix the Eggs: In a large bowl, whisk the eggs, milk (or heavy cream), salt, pepper, and a pinch of nutmeg until smooth and well-combined.
6. Combine and Bake: Pour the egg mixture evenly over the vegetables and cheese in the baking dish. Top with the remaining shredded cheese. Bake for 30-35 minutes, or until the center is set and the top is golden brown. A knife inserted into the center should come out clean.
7. Rest and Serve: Let the casserole rest for 5-10 minutes before slicing and serving. This helps it set and makes for cleaner slices.

Expert Tips for Success

Want to ensure your Spinach and Mushroom Egg Casserole is absolutely perfect? Here are a few pro tips.

• Avoid a Watery Casserole: The key is to remove as much moisture as possible from the vegetables before baking. Sauté the mushrooms until they are nicely browned, and make sure to squeeze out any excess water from the cooked spinach.
• Cheese Choices: While cheddar and Gruyère are a fantastic combination, feel free to experiment with cheeses like feta, goat cheese, or Monterey Jack.
• Don’t Overbake: Keep an eye on the casserole. Overbaking can lead to a rubbery texture. The center should be just set—it will continue to cook slightly as it rests. For another delicious eggy breakfast, try these Air Fryer Egg Toasts.

Variations and Substitutions

This recipe is a fantastic template. Feel free to customize it to your liking!

• Add Meat: For a heartier dish, add cooked crumbled sausage, diced ham, or crispy bacon to the vegetable layer.
• Different Veggies: Swap mushrooms for diced bell peppers, chopped broccoli, or sun-dried tomatoes.
• Make it Dairy-Free: Use unsweetened almond milk or coconut milk and your favorite dairy-free shredded cheese.
• Spice it Up: Add a pinch of red pepper flakes to the egg mixture for a little kick of heat. If you enjoy crustless recipes, our crustless spinach quiche is another must-try.

Make-Ahead and Storage Instructions

Make-Ahead Assembly:

You can fully assemble the casserole (without baking) the night before. Simply prepare the vegetable layer and pour the egg mixture over top. Cover tightly with plastic wrap and refrigerate for up to 24 hours. When ready to bake, remove it from the fridge while the oven preheats and bake as directed, adding 5-10 minutes to the cooking time.

Storing and Reheating Leftovers:

Store leftover casserole in an airtight container in the refrigerator for up to 4 days. Reheat individual slices in the microwave for 60-90 seconds or in the oven at 350°F (175°C) until warmed through.

Freezing Instructions:

This casserole freezes wonderfully. Let it cool completely, then either freeze the entire dish or cut it into individual portions. Wrap tightly in plastic wrap and then foil. It can be frozen for up to 3 months. To reheat, thaw overnight in the refrigerator and bake at 350°F (175°C) until hot, or microwave from frozen.

Frequently Asked Questions

Your New Favorite Breakfast Casserole!

This Spinach and Mushroom Egg Casserole is a game-changer for anyone who loves a savory, satisfying breakfast without the fuss. It’s the perfect dish to share with family and friends or to meal prep for a week of delicious mornings. Give it a try, and let us know what you think in the comments below! Don’t forget to save this recipe to your favorite board on Pinterest!

Spinach and Mushroom Egg Casserole

Spinach and Mushroom Egg Casserole (Easy & Make-Ahead!)

This Spinach and Mushroom Egg Casserole is a savory, low-carb breakfast bake packed with fluffy eggs, earthy mushrooms, and melted cheese. Perfect for meal prep, brunch, or a healthy start to your day!

Print Recipe Pin Recipe

Prep Time 15 minutes mins

Cook Time 35 minutes mins

Total Time 50 minutes mins

Servings: 8 servings

Course: Breakfast, Brunch

Cuisine: American

Calories: 250

Ingredients Equipment Method Notes

Ingredients

  

• 12 large eggs
• 1 tbsp olive oil
• 1 medium onion finely chopped
• 2 cloves garlic minced
• 8 oz cremini mushrooms sliced
• 5 oz fresh spinach
• 1 cup milk or heavy cream for a richer casserole
• 1.5 cups shredded cheese divided (cheddar or Gruyère blend recommended)
• 1 tsp salt
• 0.5 tsp black pepper
• 0.25 tsp nutmeg optional

Equipment

• 1 9x13 inch Baking Dish
• 1 Large Skillet
• 1 Large bowl

Instructions

 

1. Preheat your oven to 375°F (190°C). Grease a 9x13 inch baking dish.
2. Heat olive oil in a large skillet over medium heat. Sauté the chopped onion until soft, then add the garlic and mushrooms. Cook until the mushrooms have browned.
3. Add the spinach and cook until wilted. Drain all excess liquid from the vegetables to prevent a watery casserole.
4. Spread the vegetable mixture in the prepared baking dish. Sprinkle with half of the shredded cheese.
5. In a large bowl, whisk together the eggs, milk (or cream), salt, pepper, and nutmeg.
6. Pour the egg mixture over the vegetables. Top with the remaining cheese.
7. Bake for 30-35 minutes, until the center is set and the top is golden. Let it rest for 5-10 minutes before slicing and serving.

Notes

To Avoid a Watery Casserole: The most important step is removing moisture. Squeeze the cooked spinach with your hands or press it against a colander to remove as much water as possible.
Make-Ahead Tip: Assemble the casserole completely, cover, and refrigerate for up to 24 hours before baking. You may need to add 5-10 minutes to the bake time.