The devil is in the detail. Overbeat the eggs and the omelette will be heavy; add too much butter and it will wrinkle; use too thin a pan and it will scorch; cook too long and it will be rubbery. The end result should be "baveuse", as the French say - still runny in the middle.
3 free-range eggs
Sea salt and pepper
1 tsp snipped chives
2 tsp butter, plus extra butter for serving
Lightly beat eggs, sea salt, pepper and chives with a fork just before cooking (some cooks also add a tablespoon of milk or water).
Heat a 20-centimetre-diameter non-stick frying pan with sloping sides over medium heat, add butter, swirl well to coat, and heat until foaming.
Pour in eggs immediately and cook, using a spatula to draw back edges as they set, while tilting the pan to spill the runny egg over edges. When golden and set underneath but still a little runny on top, scatter your chosen filling (such as sliced smoked salmon) over half the omelet. Tilt the pan so the omelet slides up one side and folds over on itself, then slip it out onto a warm plate. Glaze the top with a little extra butter and whatever suits your filling (such as a spoonful of creme fraiche and sprigs of dill).
Tip According to legendary British food writer Elizabeth David in 'French Provincial Cooking': "The eggs are often beaten too savagely. In fact, they should not really be beaten at all, but stirred, and a few firm turns with two forks do the trick."