Mom's Fish Chowder
It's important to use russet baking potato as it is starchy and will help thicken the chowder.
Use 2 potatoes and 2 ribs of celery to stretch the soup for more people.
You can also add imitation crabmeat and double all ingredients (except fish of course) for a yummy crab/fish chowder.
Also feel free to exchange 1 cup clam juice for 1 cup water when expanding the recipe.
Any firm, mild white fish can work in place of the cod.