Peel the potatoes and steam for about 20 minutes. Let cool, cut into thin slices and fry in half the oil in a pan for about 5 minutes, season with salt and pepper.
Wash the leek, cut in half lengthways and cut into slices. Wash and quarter the apples, remove the core and cut into thin slices.
Remove the potatoes from the pan, add the remaining oil, leek and apple slices to the pan and sauté over a medium heat for about 5 minutes. Mix in the potatoes again and season to taste with the lemon juice, salt, pepper and spices.