THE OMELETTE:
Three eggs per person, smallish saucepan. I beat the eggs lightly and season to taste.
Heat equal parts oil and butter (so the butter doesn't burn) but not a huge amount of either or you'll end up with an oily omelette.
Wait until the butter has frothed and subsided, then add the eggs and wait five seconds for the bottom to set.
Everyone has a different technique for the next bit - the ones above sound good. Whatever works for you! I tip the pan in this direction and that whilst pushing the setting mixture up towards the centre of the pan. It means the unset eggs trickle down into the gaps. Try and do this evenly in every direction.
When it is nearly set (but a bit runny on top) I add the filling down the centre, and then flip both edges towards the centre so that they overlap slightly. I usually tip the pan in the direction that I'm flipping to help it along. There's a bit of a nack to this so it might take you a few goes. It did with me anyway :)
If I'm adding a cooked filling then I always cook it beforehand, usually in the same pan, which I wash before making the omelette itself.
THE FILLING:
If you like mushrooms, as I do, try this (amount per person):
-Two or three chestnut mushrooms, thinly sliced with the stalks removed.
-One clove of minced garlic.
-Three tablespoons of Parmesan or similar cheese.
-Black pepper.
Slowly fry as you would when making garlic mushrooms. You can add a dash of single cream if you like. Leave out the Parmesan for now.
Put in a warm bowl to one side while you make the omelette.
When the omelette is nearly set, sprinkle the Parmesan over the whole surface, and then add the garlic mushroom mixture in a line down the middle.
Flip both edges towards the middle as described above, and enjoy :)