1. Soak the salt cod for 24 hours in a large container (important because the more water, the better it desalinates).
Change the water at least 4 or 5 times.
2. In a mortar, crush a few grains of coarse salt and finely crush the peeled garlic, while poaching the cod. Cook the peeled and diced potatoes at the same time.
3. Remove the cod and crush it with a fork, carefully removing the bones. Crush the cod very finely, adding a little oil and warm milk (one spoonful of oil, one spoonful of milk) until you obtain a smooth and creamy paste.
4. Drain the potatoes when they are perfectly cooked and mash them with a real potato masher while incorporating the heavy cream. (You should obtain a smooth and creamy mashed potato).
5. Mix the mashed potatoes with the cod and smooth it out well. If the mixture is too thick, add some warm milk. Decorate with a few black olives cut in half.