courtesy of The Bon Appétit Test Kitchen

Ingredients
2 tablespoons butter
1 cup chopped leeks (white and pale green parts only)
1 12-ounce bunch thin asparagus, trimmed, cut on diagonal into 1-inch pieces (about 2 1/2 cups)
1 cup sliced stemmed shiitake mushrooms
3 eggs
1 cup diced Fontina cheese, divided
1/2 teaspoon salt
1/2 teaspoon ground black pepper
1/4 cup grated Parmesan cheese

Method

1. Preheat broiler.
2. Melt butter in heavy broiler-proof 10-inch-diameter nonstick skillet over medium heat.
3. Add leeks and sauté 4 minutes.
4. Add asparagus and shiitake mushrooms, sprinkle lightly with salt, and sauté until tender, about 6 minutes.
5. Whisk eggs, ¾ cup Fontina cheese, ½ teaspoon salt, and ½ teaspoon pepper in medium bowl.
6. Add egg mixture to skillet; fold gently to combine.
7. Cook until almost set.
8. Sprinkle remaining ¼ cup Fontina cheese and Parmesan cheese over.
9. Broil until frittata is puffed and cheese begins to turn golden, about 3 minutes.
10. Cut into wedges and serve.