Even if you buy it already desalted, it’s a good idea to soak the salt cod in cold water for 3 to 4 hours, changing the water at least twice.
Wash the potatoes thoroughly and then put them, with their skins on, into a saucepan of cold water with a pinch of coarse salt. Bring to the boil and cook them for 20-30 minutes, then test them with a fork: if it goes in easily they’re ready, otherwise continue cooking them. Strain them and remove their skin while still fairly hot, in this way it will come off easier. Squash them with a potato masher (or put them through a food mill). Use a sharp knife to remove the skin and any bones from the salt cod. Then cut it into small pieces. Heat 3 spoonful of olive oil in a frying pan, add the cod and cook until it begins to break up; transfer it into a bowl and leave to cool down well. Combine it with the egg white using a hand blender until you have a smooth mixture; then gradually incorporate the ricotta and the mashed potato. Stir thoroughly and season with salt, pepper and the chopped marjoram leaves (setting a few aside to garnish the finished dish). Clean the artichokes: cut off part of the stalk leaving just 4 or 5 cm; remove the outer, tougher petals; cut off the tip, the external part all the way round the base below the petals, and the outside of the stalk. Cut them in half, remove the “hairy” choke inside if there is any, and put them in a bowl of water with the juice of the lemon (also adding the two halves of the squeezed fruit). Remove the artichoke halves from the bowl, cook them in boiling, salted water for 5 minutes, and then strain. Fill them with the salt cod mixture prepared previously and arrange them in an oven dish greased with a spoonful of olive oil. Sprinkle the artichokes with the grated pecorino, drizzle 2 or 3 spoonfuls of olive oil over them, add a spoonful of water in the bottom of the dish and cook in a preheated oven, at 180 °C, for 20 minutes (once or twice during cooking, take the dish out of the oven and baste the artichokes with any cooking juices that have formed); for the last 2-3 minutes turn on the grill function. When a golden crust has formed, take the dish out and leave to rest for 10 minutes. Then garnish with a few marjoram leaves and serve.