This spinach mushroom onion frittata is a hearty, protein-packed egg dish that comes together in one skillet. It’s perfect for breakfast, brunch, or a quick weeknight dinner, and it’s naturally gluten-free and low-carb. The combination of earthy mushrooms, sweet caramelized onions, and tender spinach creates a savory, satisfying meal that’s easy to customize.
Ingredients
- 8 large eggs
- 1/4 cup (60 ml) whole milk or heavy cream
- 1/2 teaspoon salt
- 1/4 teaspoon black pepper
- 2 tablespoons (30 ml) olive oil, divided
- 1 medium yellow onion, thinly sliced (about 1 cup / 150 g)
- 8 oz (225 g) cremini or white mushrooms, sliced
- 3 cups (90 g) fresh spinach, roughly chopped
- 1/2 cup (50 g) shredded cheese (cheddar, Gruyère, or feta), optional
- 1 tablespoon (15 g) butter, for the pan
Instructions
- Preheat your oven to 350°F (175°C).
- In a medium bowl, whisk together the eggs, milk, salt, and pepper until well combined. Set aside.
- Heat 1 tablespoon of olive oil in a 10-inch (25 cm) oven-safe skillet over medium heat. Add the sliced onion and cook, stirring occasionally, until soft and golden, about 5–7 minutes.
- Add the remaining 1 tablespoon of olive oil and the sliced mushrooms. Cook until the mushrooms release their liquid and start to brown, about 5–6 minutes. Season with a pinch of salt and pepper.
- Add the chopped spinach and cook, stirring, until just wilted, about 1–2 minutes. Remove the skillet from heat and spread the vegetables evenly across the bottom.
- If using cheese, sprinkle it over the vegetables. Pour the egg mixture over the top, tilting the pan to distribute evenly.
- Place the skillet in the preheated oven and bake for 15–18 minutes, until the edges are set and the center is just barely jiggly. The safe minimum internal temperature for egg dishes is 160°F (71°C), per USDA FSIS guidelines—check with a food thermometer.
- Let the frittata rest for 5 minutes before slicing. Serve warm or at room temperature.
Tips
- Don’t overcook: The frittata will continue to cook from residual heat after you pull it out. Take it out when the center is just set but still slightly soft—it will firm up as it rests.
- Use a well-seasoned or nonstick skillet: This prevents sticking and makes cleanup easier. If your skillet isn’t oven-safe, wrap the handle in foil or transfer the mixture to a greased baking dish before baking.
- Substitutions: Swap the milk for a dairy-free alternative like oat milk, or use any cheese you have on hand. You can also add other vegetables like bell peppers or zucchini, but sauté them first to remove excess moisture.
- Make it ahead: Cook the vegetables the night before and refrigerate them. In the morning, just whisk the eggs and assemble.
Serving Suggestions
Serve this frittata with a simple green salad dressed with lemon vinaigrette, a slice of crusty toast, or roasted potatoes. It also pairs well with fresh fruit or a light yogurt parfait for a complete brunch spread.
Variations
- Add protein: Fold in cooked bacon, sausage, or diced ham before baking.
- Herb it up: Stir in fresh thyme, chives, or parsley for extra flavor.
- Make it dairy-free: Use olive oil instead of butter, omit the cheese, and use unsweetened almond milk.
- Spicy kick: Add a pinch of red pepper flakes or a diced jalapeño with the onions.
Storage and Reheating
Refrigerate leftovers in an airtight container for up to 3–4 days. To reheat, place slices in a skillet over medium-low heat for 2–3 minutes per side, or microwave on a plate for 1–2 minutes. You can also freeze the frittata for up to 2 months; thaw overnight in the fridge and reheat gently.
Frequently Asked Questions
Can I make this frittata without an oven-safe skillet? Yes. Cook the vegetables in a regular skillet, then transfer them to a greased 9-inch pie dish or baking pan. Pour the eggs over and bake as directed.
Why is my frittata watery? Watery frittatas usually come from vegetables that weren’t cooked long enough to release their moisture. Make sure the mushrooms are browned and the spinach is fully wilted before adding the eggs.
Can I use frozen spinach? Absolutely. Thaw it completely and squeeze out as much liquid as possible before adding it to the skillet. You’ll need about 10 oz (280 g) frozen spinach for this recipe.
How do I know when the frittata is done? The edges should be set and lightly golden, and the center should feel just slightly jiggly. A food thermometer inserted in the center should read 160°F (71°C).
Can I double this recipe? Yes, but use a larger skillet (12-inch) and increase the baking time by 5–8 minutes. Check the internal temperature to ensure it reaches 160°F (71°C).
Is this frittata keto-friendly? Yes, it’s low in carbs and high in protein. Just skip the milk or use a keto-friendly alternative like heavy cream.
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Safety notes: safe minimum internal temperatures from USDA FSIS; raw and undercooked fish guidance from the U.S. FDA. Food safety notes
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