Begin soaking the whole piece of salt cod in water three days prior to the day you want to prepare the dish
Replace the water daily and be sure to cover the salt cod completely. Place it into the refrigerator while it's soaking
Puree the onion, garlic, tomato and water in a food processor until a fine consistency
Pour a tablespoon of oil into a large frying pan and add the tomato sauce, herbs, Espelette pepper and achiote.
Simmer the sauce while preparing and cooking the cod
Drain, rinse, pat dry and then cut the salt cod into pieces about 3 x 3 inches square. The sizes of the pieces will vary based on the shape of the fish
Sprinkle the fish with two tablespoons of flour and pepper
Separate egg whites and beat until stiff
Beat egg yolks until creamy
Combine egg whites, egg yolks, two tablespoons of flour, achiote and pepper, beating for a minute or two until batter is creamy
Heat five tablespoons of oil in a frying pan until it reaches a medium high temperature
Dip each piece of salt cod in batter and fry in oil until browned (3 minutes), then remove and allow it to drain on paper towels.
Repeat until all the fish is cooked. Try to work quickly so the batter doesn't begin to separate.
Place the fish in the tomato sauce and add the potatoes and olives
Cover and heat thoroughly at a medium temperature (5-10 minutes)
Sprinkle with parsley and serve