‚PRemove the entrails and shells from the squid and rinse well. Skin the bodies and triangle tail, and mince them. Then, pound them using the back of a knife to resemble ground meat. Slice the suction cups off the legs and mince and pound them the same way. ‚QMince the onion and fry in butter until golden. Allow it to cool. ‚RMix the mayonnaise and lemon juice to make lemon mayonnaise. ‚SFor the mashed potato, boil the whole potato and remove the skin. Strain while hot, put it in a pan, and add the butter and milk. Heat over low heat. Stir constantly while heating. When it becomes smooth, season with salt and pepper. ‚TCombine the squid prepared in 1 and the onion prepared in 2 in a bowl. Add the egg yolk, flour, salt and pepper. Mix the entire ingredients together just as if you were kneading dough. ‚UDivide 5 into quarters and form each into a 1.5cm-thick round Form a hollow at the center of each. ‚VHeat some oil in a frying pan and fry 6 until both sides become crispy. ‚WPlace the squid hamburger on servings dishes and pour the lemon mayonnaise over them. Add the mashed potato, watercress and cherry tomatoes.