Ellie's Broccoli and Cheddar Frittata

4 large eggs

4 large egg whites

2 tablespoons water

2 teaspoons olive oil

1 small red onion, cut in half, then thinly sliced into half-moons

2 cups chopped cooked or thawed frozen broccoli

1/4 teaspoon salt

Freshly ground black pepper to taste

2 ounces extra-sharp cheddar cheese, shredded (1/2 cup)

Preheat the broiler.  Combine the whole eggs, egg whites, and water in a medium bowl and whisk well.  In a medium ovenproof nonstick skillet, heat the oil over medium heat. Add the onion and cook, stirring, until it begins to soften, about 3 minutes. Add the broccoli and cook for another 2 minutes. Season with salt and pepper. Pour the egg mixture over the vegetables in the skillet covering them evenly. Reduce the heat to medium-low, cover, and let cook until the egg mixture has set around the edges of the pan but is still somewhat liquid in the middle, about 8 minutes. Sprinkle with the cheese. Place the skillet under the broiler about 2 inches from the heat until the surface is set and golden brown, 1 to 2 minutes. Be careful not to overcook or the egg mixture will become tough.  Cut the frittata into 8 wedges and serve.