Peel the potatoes, cut into cubes and boil in salted water. Smash with a fork, as diluted with water in which mumbo until a smooth puree. Leeks cut into in small pieces and add to the potatoes. If needed, add a little salt. Pour the mayonnaise and stir to give a good homogeneous mixture. Allow to stand in the refrigerator, as the longer the standing as a better joint. Optional can add a little parsley.