1) Sauté potato slices in boiling hot tap water for five minutes and remove with a slotted spoon.
2) Dissolve butter in frying pan, add juice of one lemon and sugar and heat until sugar is dissolved.
3) Add a small amount of cognac to the potato slices and sauté at low temperature until the slices are soft.
4) Add grated lemon skin and spread on a plate with lemon slices.