This is one of Spain's most delicious & famous soups, I would say of Basque origin.

Leek and Potato Hotpot (Purrusalda)

This stew is a meal in itself because it contains proteins, carbohydrates, and fats in the right proportions. If served with not much stock it is a good midday dish or, a little soupier, it makes a good starter for dinner. Best made well in advance.
Servings: 4

5 oz salt cod
1 1/2 lb leeks
1/2 cup oil
2 cloves garlic
2 1/4 lb potatoes
Salt
Pepper
Parsley

Soak the cod in cold water for 24 hours, changing the water every eight hours. Drain and place in a pan. Cover with cold water and bring to a boil. Remove the pan from the heat and cover. When no longer hot, lift out the cod (keeping the cooking water), remove any bones and cut into cubes. Remove the green leaves from the leeks, wash well and cut into even-sized pieces. Fry the peeled garlic cloves until golden. Add the leeks and fry lightly, then add the peeled and washed potatoes in medium-sized pieces.

Add the cod and cover everything with the water used to cook the cod. Simmer for 35 minutes. Add salt if necessary and pepper and serve very hot, sprinkled with chopped parsley. Tradition has it that the potatoes should be broken into pieces rather than cut. This is done by inserting a knife far enough for you to be able to pull the pieces apart with your hands. The reason for this is perhaps that this way the potatoes release their starch more easily which makes the sauce thicker.

Source: María Jesús Gil de Antuñano