Cut the onion in half, then thinly slice each half and separate the layers into half-moon shapes.
Peel and wash potatoes.
Slice them into thin rounds.
Rub them on a clean cloth to get them as dry as possible.
Heat two tablespoons of olive oil in an eight-inch non-stick frying pan.
When it is smoking hot, add the potatoes and onions.
Toss them around in the oil to get a good coating.
Add a generous sprinkling of salt and freshly crushed pepper.
Cover frying pan with a lid.
Cook potatoes and onions until tender.
Turn them over halfway through and shake the pan from time to time.
Do not let them brown.
Break the eggs into a large bowl and, using a fork, whisk them lightly.
It is important not to over beat them.
Add salt and pepper to taste.
When the potatoes and onions are well stewed in the oil, quickly transfer them to the eggs in the bowl.
Put the frying pan back on heat.
Add the remaining oil and increase heat to medium.
Mix the potato and eggs thoroughly.
Pour the whole lot into the frying pan.
Lower heat to minimum immediately.
Cover and cook.
Uncover every now and then and draw the edge in gently with a knife to give a firm shape to the omelette.
When the surface looks firm and dry, turn and cook the other side.
Cook further to two minutes and remove from heat.
Let it rest for five minutes.
Cut into wedges and serve sandwiched in chunks of crusty French loaf.