This spinach and mushroom egg casserole is my go-to for weekend brunch or when I want to meal prep breakfast for the week.
It’s packed with veggies, super simple to make, and tastes amazing right out of the oven or even reheated. You just sauté some mushrooms and spinach, pour eggs over it, bake, and boom—done!
Why I Love This Recipe
This is one of those dishes that just always works. Whether I’m serving it to friends or saving it for myself, it comes out perfect every time.
- You only need one pan and one baking dish
- It’s loaded with flavor but still light and healthy
- Super customizable—use any veggie or cheese you have
- Great for breakfast, lunch, or dinner
I first made this on a Sunday morning when I had leftover mushrooms and spinach in the fridge. Didn’t want to waste them, so I whipped up this casserole, and now it’s a regular in my kitchen.
What You’ll Need
- 8 large eggs
- ½ cup whole milk
- 1 cup shredded mozzarella cheese
- 1 tbsp olive oil
- 1 small onion, diced
- 2 cups mushrooms, sliced
- 2 cups fresh spinach
- ½ tsp garlic powder
- ½ tsp salt
- ¼ tsp black pepper
- Cooking spray or extra oil (for greasing the dish)
Pro Tips
- Sauté the mushrooms until the liquid is gone—this keeps your casserole from getting watery.
- Let the casserole rest for 5 minutes after baking to set up nicely.
- Use pre-shredded cheese to save time.
- Chop spinach roughly if you want smaller bites.
- Add a pinch of chili flakes for a kick.
Tools Needed
- 9×13 baking dish
- Skillet
- Mixing bowl
- Whisk
- Cutting board and knife
- Measuring cups and spoons
- Cooking spray or brush
Substitutions and Variations
- Use kale instead of spinach (just cook it a little longer)
- Swap mozzarella for cheddar, feta, or pepper jack
- Add chopped tomatoes, bell peppers, or cooked bacon
- Use almond milk or oat milk for dairy-free
Make Ahead Tips
- You can sauté the veggies and mix the egg base the night before.
- Pour everything into your greased dish, cover, and refrigerate overnight. In the morning, just bake it straight from the fridge (add 5 minutes to bake time).
How to Make It
Makes 6–8 servings
Cook Time: 35 minutes
Prep Time: 15 minutes
Step 1: Sauté Onion and Mushrooms
Heat 1 tbsp olive oil in a skillet over medium heat. Add 1 small diced onion and 2 cups sliced mushrooms. Cook for 6–8 minutes, until soft and mushrooms have released all their liquid.
Step 2: Add Spinach and Seasoning
Add 2 cups fresh spinach, ½ tsp garlic powder, ½ tsp salt, and ¼ tsp black pepper to the skillet. Stir until spinach is wilted, about 1–2 minutes.
Step 3: Grease Baking Dish
Spray a 9×13 baking dish with cooking spray or brush it lightly with oil.
Step 4: Add Veggie Mix to Dish
Spread the cooked mushroom, onion, and spinach mix evenly in the greased dish.
Step 5: Whisk Eggs and Milk
In a mixing bowl, whisk 8 large eggs and ½ cup whole milk until smooth.
Step 6: Pour Egg Mixture into Dish
Pour the egg and milk mixture evenly over the veggies in the baking dish.
Step 7: Add Cheese
Sprinkle 1 cup shredded mozzarella cheese evenly over the top.
Step 8: Bake
Place the dish in the oven and bake at 375°F for 30–35 minutes, or until the center is set and the top is lightly golden.
Step 9: Let Cool and Serve
Let the casserole rest for 5 minutes, then slice and serve warm.
Leftovers and Storage
- Store slices in airtight containers in the fridge for up to 4 days
- Reheat in the microwave or oven until warm
- Can be frozen in slices—wrap individually and store up to 2 months
Macros (Per Serving – Based on 6 Servings)
- Calories: 230
- Protein: 16g
- Carbs: 5g
- Fat: 17g
- Fiber: 1g
Why This Recipe Works (Quick Science)
Eggs act as a binder and puff up while baking, creating a light, fluffy texture. Milk adds creaminess and prevents the eggs from becoming rubbery. Cooking the veggies first removes moisture so the casserole sets up without being soggy. Melting cheese on top finishes everything with a golden, flavorful crust.
Common Mistakes
- Adding raw mushrooms – They’ll release water and make the casserole soggy.
- Skipping the rest time – It helps the casserole firm up for clean slices.
- Overbaking – This can make the eggs rubbery. Pull it once the center is just set.
What to Serve With
- Toasted sourdough or English muffins
- Fresh fruit or a fruit salad
- Crispy hash browns or roasted potatoes
- Iced coffee, tea, or a fresh juice
FAQ
Can I use egg whites?
Yes, use 1 cup of liquid egg whites or replace some of the eggs.
Can I make this dairy-free?
Use a plant-based milk and skip the cheese or use a dairy-free version.
Can I add meat?
Definitely! Cooked bacon, sausage, or ham all work great.
Is this good for meal prep?
Yes! Just slice, store, and reheat during the week.
Final Thoughts
This spinach and mushroom egg casserole is simple, tasty, and makes mornings so much easier. It’s hearty, healthy, and perfect for making ahead. I hope it becomes one of your regulars too. Try it out and let me know how it went—I’d love to hear your twist on it!