Put a non-stick frying pan over a low heat. Cook the shallots slowly in the oil and butter until soft and caramelised.
Add the potatoes to the pan, then cover and cook for a further 15 minutes, stirring occasionally. When the spuds are soft, add a pinch of salt and white pepper. Crush the garlic cloves (or add the wild garlic) and stir into the mixture, along with the grated nutmeg. Then add the beaten eggs and egg yolks.
Cover with a lid (or a tin foil cartouche if, like me, you can never find the right lid!) and leave the tortilla to cook slowly. After 15 minutes, the edges and base will be golden brown, and the top will be set, but the middle still showing a wobble. To finish cooking it needs to be flipped: slide it onto a plate, put another plate on top, turn it over and slide it back into the pan to finish cooking for a further 5 minutes.