Pre-heat a nonstick skillet** over medium for a few minutes, until it feels warm when you hold your hand a few inches from the surface of the pan.
In the meantime, in a medium bowl, whisk to combine the eggs, water, and salt until well-blended. No streaks of egg white should remain.
Add enough butter to coat the bottom of the skillet (1-2 tsp), then quickly add the beaten egg. Turn the heat to medium low.
After some of the egg has set, lift the edges of the omelette and tilt the pan to allow the liquid uncooked egg to come into contact with the hot pan and cook.
When the egg is almost set, add any desired filling, and cook for a minute, to melt any cheese or warm through any of the filling ingredients.
Fold the omelette over to enclose the filling, then serve and enjoy while warm.
*I like a thinner omelette, and use 2 eggs. If you want a thicker, more traditional omelette, use 3 eggs and 3 tbsp water.**I use a 10" pan to cook the omelette. If you want a thicker omelette, one way is to add more egg, but another is to use a smaller skillet, like an 8."For filling ingredients, some type of cheese is great for "glueing" the omelette together and also for moisture/flavor. For cooked meats, I like adding Italian crumbled sausage, bacon, and ham. Numerous vegetables are great for omelettes, but my favorites are sauteed mushrooms, sauteed spinach, fresh chopped tomatoes, and cooked broccoli.