Put the prepared cod in a pot of fresh cold water, bring to a boil and simmer until it flakes at the touch of a fork, about 5 minutes. Drain, cool, remove any bones, and place in the food processor.
Whisk the egg yolk and milk together with a fork. Sift in the flour and baking powder and mix to a paste. Add this to the food processor with the fish and pulse 1 minute until pasty and shredded. Stir in the onions, chives, and hot pepper. Beat the egg white to peaks and fold it in.
Heat the oil in a high-sided pot until a piece of batter dropped in sizzles instantly. Fry a small piece and taste. Adjust the seasonings as necessary. Fry a few beignets at a time until dark golden, crisp and light, about 3 minutes. Drain on paper towel.