Bring a large pan of cold water to the boil. As soon as the water starts to boil, remove from the fire and poach the cod for 10 minutes. Drain and flake the fish.
Wash the potatoes. Boil them for 30 minutes starting with cold water. The potatoes should be cooked through.
Drain and peel the potatoes, then mash them.
Sift the flour, make a well in the centre and gently stir in the water while mixing the mixture to obtain an even batter.
Crush the garlic and finely chop the onion and parsley. Mix them with the flaked cod and season with chilli pepper. Add the batter, mashed potatoes, and lime. Mix well.
Set aside for 30 minutes at room temperature.
Use two teaspoons to form small fritters. Fry them in hot oil until golden brown. Drain the fritters on kitchen paper.
Chop the dill, shallot and gherkin finely. In a bowl, mix the yoghurt with the capers, chopped gherkin, lime juice and chopped dill. Season to taste with salt and pepper. Serve with the balls.