Soak the salt cod in water for 36 hours, changing the water every 12 hours. Drain it, pull off the skin, remove the bones, and fry it briefly in olive oil.
Sauté the spinach in olive oil with salt until it wilts and the released liquid evaporates.
Peel the potatoes, slice them into medium-thick rounds, fry them in olive oil, then drain.
Preheat the oven.
In an earthenware dish, layer potatoes, then the cod, and cover with the spinach. Bake in the oven at 80 degrees for half an hour.
Serve on plates, topped with the chopped hard-boiled egg and olives.