Heat the oil in a non-stick frying pan, measuring about 18 cm (7 in) across the base. Add the potatoes, onion and garlic. Stir together until coated in the oil, then cover the pan. Cook gently, stirring from time to time, for 10 to 15 minutes or until the potato is soft. Season with salt.

Add the chorizo to the potato mixture. Season the eggs and pour on to the potato mixture. Cook over a moderate heat for 5 minutes or until beginning to brown at the edges and the egg is about three-quarters set. Put the pan under a preheated grill to brown the top.The egg should be a little soft in the middle as it continues to cook and set as it cools.

Carefully loosen the tortilla round the edge and underneath with a palette knife or fish slice, cut into wedges and serve.