I learned to prepare this meal from my mother in Mexico City. She learned it from her mother, Juanita who learned it from her mother, Esther. We cook it for Christmas dinner although there are no religious reasons for why. It is a laborious dish and nobody in the family has the patience to cook it more than once a year. —Intelatin
Soak the Cod overnight to remove the salt. Rinse the next day and re-soak. Rinse the next day and re-soak.
Once the Cod has been soaked for three days, rip the fillets with your hands to produce a small mountain of cod pieces.
Meanwhile, peel and mince garlic until your fingers bleed.
Meanwhile, peel many small potatoes to remove skins.
Meanwhile, place tomatoes on a "comal" to tan for a bit.
I would razor onions as well at this point but the recipe forbids it. If it were allowed, now would be the time to add olive oil to the pot with garlic (and onions).
Then, add the tomatoes and a few cans of tomato paste. You want the color to be light red. Stir. Once you think the foundation is ready, add the Cod. Then, add the potatoes. Stir occasionally and bring to boil. Let sit for several hours and then bring to boil again. Let sit for a day and then eat the next day.
Add olives and mild chiles for garnish.
Serve with a fresh bolillo at its side on a plate shaped like a fish. See picture...