Heat a small, preferably nonstick, frying pan over a high heat. Whisk two eggs and two teaspoons of milk or water until thoroughly mixed but not too frothy. Season with salt and pepper.
Add two teaspoons of oil to the pan. As soon as it sizzles, pour in the egg mixture. If you’re using a filling, such as herbs or cheese, add it now.
Use a spatula to quickly pull the edges of the omelette towards the centre of the pan, while tilting the pan around so the raw egg runs towards the edges. Cook for about 30 seconds until most of the egg is set; the centre will still be slightly soft, but it will set by the time it’s ready to serve.
Flip one side of the omelette over the centre, then slide the omelette onto a warm serving plate.