Two days ahead, soak dry cod for 2 days in a bowl of water in fridge. Change water twice a day. Remove any skin and all bones. Skip this step if using frozen cod.
Bring large pot of water to a boil. Add fish and boil until tender and flaky (test with fork). Drain well.
Mix yeast with water and allow to sit for 5 minutes.
Add another 1 1/2 cups warm water and stir.
Add enough flour just to make a very soft (thick, creamy) dough.
Shred the fish (with two forks) well. Mix into the batter.
Stir in a pinch of salt and pepper. If using frozen cod, be more generous with the salt. Mix well. Taste to see if you need more salt.
Cover and let rise for 1/2 hour.
In large frying pan, heat about 1/4" to 1/2" olive oil over medium/high heat. Fry fish batter by tablespoons-ful (like pancakes), until light golden-brown on both sides. Continue until batter is finished.
Strain on paper towels.
Leftovers can be covered in the refrigerator for about a week. Warm up in the oven at 350 degrees F, wrapped loosely in foil for a few minutes until warm throughout.