Soak the fabes in cold water for at least 8 hours before you prepare them. Do the same with the bacon and the lacón to remove some of the salt.
Clean the leeks. To do so, cut most of the green part as well as the bottom end. Peel some of the outer leaves off, and wash it carefully making sure that there is no trace of sand or soil remaining. Peel the carrot. Cut them into big pieces.
Heat about two tablespooons of olive oil in a big pot. Add the chicken, leeks and carrot and stir it well for about one minute. Add boiling water (enough to cover your ingredients). Boil for at least 30 minutes.
Remove all the ingredients, strain it and keep the broth. Once your broth is cold, remove the greasy layer that you will find on top.
Strain the Fabes, bacon and lacón and throw them in a big pot. Cover everything up with the chicken broth and heat up.
Chop an onion and garlic cloves and add them as well. As soon as the broth is boiling you need to start removing the greasy foam with a spoon periodically.
Lower your heat as much as possible, taking into account that the broth needs to keep boiling. Boil everything for about 2 or 2 and a half hours. Just remember to remove the foam from time to time.
A bit before the Fabes are ready, boil some water in a different pot. Add the chorizos and morcilla and boil for about 15 minutes.
Add the chorizo and morcilla to the Fabes, along with 2 or 3 tablespoons of the grease you will obtain from the pot that you just used to boil the morcillas and chorizos. Boil everything together, adding the saffron after five minutes, and stirring softly with a spoon for about 20 minutes.