Boil potatoes in their skins until tender. Cool, peel and mash into a puree. Fill the mackerel fillet with milk, cover and cook for 5 minutes. Then grind.
Peel the onion, finely chop and fry in 1 tbsp. l. oil, add paprika and cook for 3 minutes, remove from heat, let cool. Mix potatoes, fish, onion, cilantro and lemon juice.
Divide the mass into 8 parts. Dip each cutlet in the beaten egg, then in the chopped peanuts. Cover with cling film and refrigerate for 30 minutes. Fry cutlets in hot oil for 4 minutes. from each side.