In a covered medium saucepan cook potatoes in a small amount of boiling lightly salted water for 10 to 12 minutes or until tender; drain. In a medium bowl beat together the whole eggs, egg whites, chives, Parmesan cheese, milk, and black pepper. Stir in potatoes; set aside.
In a large nonstick skillet cook onion in hot oil over medium heat about 5 minutes or until tender. Add Swiss chard. Cook about 15 minutes or until liquid is evaporated, stirring frequently.
Pour the egg mixture over Swiss chard mixture; do not stir. Cook over medium-low heat. As the egg mixture sets, run a spatula around edges of skillet, lifting egg mixture so the uncooked portion flows underneath. Continue cooking and lifting edges until the egg mixture is almost set (top will be wet). Cover and cook about 3 minutes more or just until top is set. Cut into wedges. Serve immediately. Makes 6 servings.