If using bacalao or a salty white fish you need to soak fish in water overnight or for 2 hours, changing water every 15 minutes. If using a not as salty fish like haddock, just soak for 30 minutes. Start to boil water. Peel & cut potatoes, put in a bowl with water (to prevent browning) until you are ready. Boil water, and put fish & potatoes in (you can separate them if you want). Let boil for 20-25 minutes, test with fork.