Skillet Cheddar-Chive Frittata with Mushrooms and Toast

Steps

1. Heat the oven to broil with a rack about 6 inches below the element. Slice the mushrooms and green onion, keeping the white parts and green tops separate, and shred the cheddar.
2. In a bowl, whisk the egg, egg white, milk, salt and black pepper until smooth. Stir in half of the cheddar and half of the green onion tops.
3. Heat the olive oil in a 10-inch oven-safe nonstick skillet over medium-high heat. Add the mushrooms and cook without stirring for 3 minutes, then stir and cook 3 to 4 minutes more until browned. Add the green onion whites and cook 1 minute.
4. Turn the heat to medium-low, pour the egg mixture over the mushrooms and cook undisturbed for 6 to 8 minutes, lifting the edges now and then so egg flows underneath, until the edges are set and the center is still slightly wet.
5. Scatter the remaining half of the cheddar over the top and slide the skillet under the broiler for 2 to 3 minutes, until puffed, golden and set in the center at 160°F (71°C).
6. While the frittata broils, toast the bread.
7. Let the frittata rest 3 minutes, sprinkle with the remaining half of the green onion tops, cut into 4 wedges and serve each with 2 slices of toast.