Preheat broiler to high. Combine egg whites, eggs, salt, pepper, and milk; stir with a whisk.
Heat a 9-inch cast-iron skillet over medium heat. Sauté mushrooms and leeks in olive oil until tender.
Layer in thyme and green onions.
Sprinkle with shredded fontina cheese.
Carefully pour egg mixture over cheese. Cook over medium heat 5 to 6 minutes or until eggs are partially set; then broil 5 inches from heat for 2 to 3 minutes or until browned and almost set.
MyRecipes is working with Let's Move!, the Partnership for a Healthier America, and USDA's MyPlate to give anyone looking for healthier options access to a trove of recipes that will help them create healthy, tasty plates. For more information about creating a healthy plate, visit www.choosemyplate.gov
This is definitely a fast and easy dish, but we found it to be a little bland. Two ounces of cheese is not much for four servings (a half ounce per serving? really?), so I doubled that but it didn't help much. We ended up sprinkling a lot of red pepper flakes on top.