1. Soak the salt cod in a large container for minimum 24 hours. Change. the water a minimum of 4 times. The cod is ready when the cod against your tongue is clean (not salty, salty) and the water pure. The morning before the night after is usually good timing. Likewise with you chickpeas, they will double in size so allow enough water to allow swelling. Soak over night 12 -18 hours.
2. Drain chickpeas and add to a saucepan, allow 1/3 more water to cover. Crush garlic clove with the the flat of your knife or the palm of your fist and add to water with 2 bay leaves. Bring the chickpeas to a simmer and then turn to lowest heat. Skim off the scum/foam and then leave to lightly bubble for 2-3 hours. You will need to add more water at some point, do not let it go dry (no seasoning at this point). The chickpeas usually take 3 hours to cook - I like a soft bite. Taste after 2 hours and so
3. Once cooked, turn off and leave in residual water. I like the cooking liquid to just be covering the chickpeas by the end. Put passata in a small saucepan with olive oil and reduce by 1/3 for 2o minutes at a light bubble this can be prepared in advance.
4. Slice the onions and fry 3/4's of them on a low heat with oil. A heavy bottomed pan is best for this, after 15/2o minutes when they start to turn golden, add a decent splash of white wine or cider vinegar, turn up the heat and allow all the liquid to evaporate for a few minutes and then turn the heat off. Add the onions and reduced passata to the chickpeas and turn the heat on to low. As the chickpeas, onions and passata start their alchemy, place the remaining onion, pepper corns, bay leaf and chopped potato to a pan, add the salt cod and fill with milk to cover. Put