Spinach Mushroom Frittata Recipe

Overview

This spinach mushroom frittata has softly set eggs, browned mushrooms, tender spinach, and a lightly golden cheese topping. Cooking the mushrooms until their released moisture evaporates keeps the frittata flavorful rather than watery.

The mixture starts on the stovetop and finishes in the oven, so use a well-seasoned cast-iron or other ovenproof skillet. Serve it warm, at room temperature, or chilled with toast and a crisp salad.

Ingredients

• 1 tablespoon olive oil
• 8 ounces cremini or white mushrooms, wiped clean and thinly sliced
• 1/2 medium yellow onion, finely diced
• 2 garlic cloves, finely minced
• 5 ounces baby spinach, roughly chopped if the leaves are large
• 8 large eggs
• 1/2 cup whole milk
• 1/2 teaspoon kosher salt, plus more for the vegetables if needed
• 1/4 teaspoon freshly ground black pepper
• 1/4 teaspoon dried thyme
• 1/2 cup shredded Gruyère, sharp cheddar, or mozzarella, divided
• 1 tablespoon chopped fresh parsley or chives, for serving, optional

How to make it

1. Heat the oven and prepare the eggs. Heat the oven to 400°F. In a medium bowl, whisk the eggs, milk, kosher salt, black pepper, and dried thyme until the yolks and whites are fully blended. Stir in 1/4 cup of the shredded cheese.

2. Brown the mushrooms. Heat a 10-inch ovenproof skillet over medium-high heat. Add the olive oil, then the mushrooms in an even layer. Cook for 5 to 7 minutes, stirring every minute or so, until the mushrooms have released their moisture and developed browned edges. If the skillet looks dry before the mushrooms soften, reduce the heat slightly rather than adding a large amount of oil.

3. Cook the onion and garlic. Add the diced onion to the skillet and cook for 3 to 4 minutes, until softened and lightly golden. Add the garlic and cook for 30 seconds, just until fragrant.

4. Wilt and dry the spinach. Add the spinach by handfuls, tossing it with the mushroom mixture. Cook for 1 to 2 minutes, until the leaves are wilted and any visible liquid has cooked off. Spread the vegetables into an even layer. The skillet should not contain a puddle of moisture before the eggs go in.

5. Add the egg mixture. Pour the seasoned eggs over the vegetables. Gently tilt the skillet so the eggs flow into the gaps, then cook undisturbed over medium-low heat for 2 to 3 minutes. The edges should begin to look opaque while the center remains loose.

6. Finish in the oven. Sprinkle the remaining 1/4 cup cheese over the top. Transfer the skillet to the oven and bake for 8 to 12 minutes, depending on the depth of the skillet. The frittata is done when the edges are set, the center has only a slight wobble when gently shaken, and no liquid egg remains on the surface. For a fully set center, bake until the eggs reach 160°F in the middle.

7. Rest and serve. Let the frittata rest in the skillet for 5 minutes. It will finish setting as it cools and will be easier to slice. Sprinkle with parsley or chives, cut into wedges, and serve warm or at room temperature.

Expert tips

• Prevent a watery frittata: Do not rush the mushrooms or spinach. Mushrooms should look browned rather than pale and wet, and spinach should be wilted with no pooled liquid before the eggs are added.
• Use the right skillet: A 10-inch skillet gives a frittata about 1 inch thick. A larger skillet will make a thinner frittata and shorten the oven time; a smaller skillet will make it thicker and require more time.
• Avoid rubbery eggs: Pull the frittata from the oven as soon as the center is barely set. Overbaking continues to firm the eggs and can make them tough.
• Substitute thoughtfully: Frozen spinach works if it is thawed and squeezed very dry; use about 1/2 cup after squeezing. For dairy-free frittata, replace the milk with unsweetened, unflavored plant milk and omit the cheese or use a dairy-free alternative.
• Change the cheese: Feta adds a salty, tangy finish, while Parmesan gives a sharper flavor. If using a salty cheese, reduce the added kosher salt slightly.
• If your skillet is not ovenproof: Cook the vegetables in a skillet, then transfer them to a greased 9-inch pie dish. Pour the egg mixture over them, add the cheese, and bake at 400°F for about 18 to 22 minutes, until the center is just set.
• For another vegetable-forward meal: The same mushroom-and-spinach combination also works well in a spinach mushroom quesadilla, where cooking off excess moisture helps the filling stay crisp rather than soggy.

Serving and storage

Serve slices with buttered toast, roasted potatoes, fresh fruit, or a simple green salad. A spoonful of sour cream, plain yogurt, salsa, or hot sauce can be added at the table.

Cool leftovers promptly, then refrigerate them in a covered container. Eat within 3 days and reheat individual slices in the microwave in short intervals or in a 325°F oven until warmed through. The frittata can also be served cold or at room temperature. Do not leave it at room temperature for more than 2 hours.

Frequently asked questions

Can I make this spinach mushroom frittata ahead of time?

Yes. Bake it up to 1 day ahead, cool it, cover it, and refrigerate it. Serve it chilled, at room temperature, or reheat slices gently in a low oven so the eggs do not become rubbery.

Why is my frittata watery?

The vegetables likely released more moisture than they had time to cook away. Brown the mushrooms until their liquid evaporates, and cook the spinach until no liquid pools in the skillet before adding the eggs.

Can I use frozen spinach?

Yes. Thaw it completely, squeeze it very dry in a clean towel or with your hands, and use about 1/2 cup of the squeezed spinach. Adding it wet can prevent the eggs from setting cleanly.

How do I know when a frittata is done?

The edges should be opaque and set, the center should have only a slight wobble, and the surface should contain no liquid egg. If using a thermometer, the center should reach 160°F.

Can I bake this without a cast-iron skillet?

Use any ovenproof 10-inch skillet. Alternatively, transfer the cooked vegetables to a greased 9-inch pie dish, add the eggs and cheese, and bake at 400°F for about 18 to 22 minutes.

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