1.Beat egg whites in large bowl with electric mixer until soft peaks form. Combine egg yolks, parmesan and half the chives in another large bowl. Gently fold whites into yolk mixture.
2.Combine ham and gruyère in medium bowl.
3.Heat one-quarter of the butter in small frying pan, add one-quarter of the egg mixture, sprinkle with one-quarter of the ham mixture. Cook over medium heat until mixture is almost set. Fold omelette in half, transfer to plate, cover to keep warm.
4.Repeat step 3 to make a further three omelettes. Serve omelettes sprinkled with remaining chives.