Preparation

• Preheat broiler.
  Melt butter in heavy broilerproof 10-inch-diameter nonstick skillet over medium heat. Add leeks and sauté 4 minutes. Add spinach and mushrooms, sprinkle lightly with salt, and sauté until tender, about 6 minutes.
  In a medium bowl, Whisk eggs, 3/4 cup Fontina cheese, 1/2 teaspoon salt, and 1/2 teaspoon pepper. Add egg mixture to skillet; fold gently to combine. Cook until almost set. Sprinkle remaining 1/4 cup Fontina cheese and Parmesan cheese over. Broil until frittata is puffed and cheese begins to turn golden, about 3 minutes. Cut into wedges and serve.