Spinach and Mushroom Frittata

Ingredients

• 8 large eggs
• 1/4 cup whole milk
• 1 tablespoon Dijon mustard
• 2 teaspoons chopped fresh thyme
• 1/2 teaspoon garlic salt
• 1/2 teaspoon black pepper
• 1/4 teaspoon kosher salt
• 4 ounces Fontina cheese, shredded (about 1 cup)
• 8 ounces sliced mixed fresh wild mushrooms (such as cremini, shiitake, button, and/or oyster mushrooms); the Test Kitchen used two 4-ounce packages of cleaned mixed mushrooms
• 2 tablespoons olive oil
• 1/2 cup sliced shallots (from 2 medium [2 ounces total] shallots)
• 5 ounces fresh baby spinach, coarsely chopped (about 4 cups)

Method

1. Preheat oven to 400°F with rack in upper third position. Whisk together eggs, milk, mustard, thyme, garlic salt, pepper, and kosher salt in a medium bowl. Fold in cheese. Set aside.
2. Heat a 10-inch ovenproof nonstick skillet over medium-high. Add mushrooms and oil; cook, stirring often, until mushrooms start to brown, about 2 minutes. Add shallots; cook, stirring occasionally, until starting to soften, about 4 minutes. Add spinach in batches, stirring until wilted after each addition. Reduce heat to medium.2 min timer
3. Pour egg mixture into skillet, and tilt skillet to distribute egg evenly over vegetables. Cook over medium until eggs around edges of skillet begin to set, 1 to 2 minutes. Remove from heat.2 min timer
4. Transfer skillet to preheated oven. Bake until frittata is puffed and set, 10 to 12 minutes. Remove from oven. Serve hot, warm, or at room temperature.12 min timer