Boil the potatoes and while they are cooking prepare a sauce by putting the cheeses (or cheese and yoghurt, if using) in a blender with the olive oil, lemon juice, garlic, salt and pepper. Add the milk very slowly at the end so that the mixture is not too thick nor too liquid. Add the Tabasco sauce if you like.
Purée the potatoes, adding a little more olive oil. Season and shape into a round. Place the lettuce leaves or tomatoes on a large platter. Put the potato on this, cover with the cream mixture and finish with the slices of hard-boiled eggs and olives around the plate.