Put a knob of butter into a pan the size you want your omelette to be. I use a fairly small pan for a 2 egg omelette. Heat the butter until it is slightly bubbling and then turn down the heat to the lowest setting. There should be just enough butter to have a coating. In the past I didn't use quite enough and it turned more into scrambled eggs.
Break 2 eggs into a container and use a fork to beat them together.
Pour the beaten egg into the pan and move it around until the bottom of the pan is covered. Allow it to slowly cook on low for a few minutes until the centre begins to cook. If you use a spatula to slightly push the bottom of the omelette around, it should not stick to the bottom of the pan. Sprinkle a pinch of salt around the surface of the egg.
When the centre begins to look as if it is cooking, it looks as if it is setting. Place chopped tomatoes on one half of the omelette to allow it to be folded over more easily.
By this stage, you should be able to lift up your pan, shake it slightly and it should move around in the pan. Let it cook for a couple more minutes until you take a lifter and fold one half of the omelette over upon itself. I use a fork in one hand and the lifter in the other to get it more even.
Cooking for a further minute, turn it over and cook until the surface on both sides is a golden brown colour.