INGREDIENTS
- 12 large eggs 1 carton
- ½ cup milk
- 1 teaspoon kosher salt divided
- ¼ teaspoon ground black pepper
- 2 tablespoons olive oil divided
- 1 shallot finely chopped
- 2 cloves garlic minced
- 2 sprigs fresh thyme
- 8 ounces cremini mushrooms sliced
- 2 cups fresh spinach
- 1 cup shredded gruyère cheese
- Grated Parmesan cheese optional, for topping
EQUIPMENT
- Cast Iron Skillet
INSTRUCTIONS
- Preheat oven to 425°F.
- Whisk the eggs, milk, ½ teaspoon salt, and pepper in a large bowl.12 large eggs,½ cup milk,1 teaspoon kosher salt,¼ teaspoon ground black pepper
- Heat 1 tablespoon of oil in a large oven-safe skillet over medium heat.2 tablespoons olive oil
- Add in the shallot and ¼ teaspoon salt, and sauté until softened, about 3-4 minutes.1 shallot
- Stir in the garlic and thyme leaves and cook until fragrant, about 1 minute.2 cloves garlic,2 sprigs fresh thyme
- Add in the mushrooms and ¼ teaspoon salt, and cook until softened and the excess liquid has been evaporated, about 3-5 minutes.8 ounces cremini mushrooms
- Stir in the spinach and cook until wilted, about 3 minutes.2 cups fresh spinach
- Transfer the mushroom mixture to a plate or bowl.
- Heat another tablespoon of oil in the skillet and swirl it around until it covers the bottom of the pan.
- Pour the egg mixture into the pan.
- Add in the mushroom and spinach mixture in an even layer over the eggs.
- Sprinkle gruyère cheese over the top.1 cup shredded gruyère cheese
- Transfer the skillet to the oven, and bake for 15 minutes, until the eggs have just set.
- Top with additional fresh thyme and grated Parmesan cheese.Grated Parmesan cheese
NOTES
- You can use boxed egg whites or a vegan egg substitute in place of the eggs.
- Feel free to use whatever milk you like, such as skim, 2%, whole, or plant-based.
- You can use butter in place of the olive oil.
- You can use rosemary or tarragon in place of the thyme.
- Feel free to use your favorite variety of mushrooms.
- You can use Swiss cheese in place of the gruyère.
- I recommend using a cast-iron skillet for the most even cooking.
- Take care not to burn the shallot or garlic; this could lead to a bitter-tasting frittata.
- Bake only until the eggs have just set; otherwise, the eggs may end up rubbery.
- Nutritional information does not include optional ingredients.
Storage: Store mushroom frittata in an airtight container in the refrigerator for up to 4 days or in the freezer for up to 2 months.

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