150g Manzanilla olives, halved
500g salt cod
80ml olive oil, plus 2-3 tbsp to fry the tortilla
2 large white onions, finely sliced
2 sprigs rosemary, leaves stripped
6 medium free-range eggs
Handful flat leaf parsley, finely chopped
Soak the cod in cold water, skin side up, for 24 hours, changing the water a couple of times.
Heat the oil in a large pan and gently fry the onions for a couple of minutes. Cover with a lid and cook over low heat for 20 minutes until really soft. Remove the lid and add the rosemary and cook for a further 20-25 minutes until really caramelised and sticky.
Meanwhile, remove the skin from the cod and flake into large pieces. Beat the egg with plenty of black pepper and gently fold in the warm onions, cod, olives and parsley.
Heat 2-3tbsp more of the olive oil in a 23cm nonstick frying pan and pour in the egg mixture. Swirl the pan over a hot heat until it starts to catch around the edges then reduce the heat and cook for 4-5 minutes until it starts to set around the edges but stays quite loose in the middle.
Cover the pan with a flat lid or board, turn the tortilla carefully onto it, don’t worry that it is still quite runny, it will all come back together when you continue to cook it. Slide the tortilla back into the pan then put the pan back on a low heat. Use a spatula to tuck the edges of the tortilla under to give it its characteristic curved look. Cook for a couple of minutes, then turn onto a board and serve. It should still be lovely and juicy in the middle when you cut into it