Boil potatoes, whole and with skins on, until soft but firm.
Turn off, drain the potatoes, and let cool.
When the potatoes are no longer boiling, preheat the oven to 190C degrees (374F).
Remove the skins from the potatoes and cut them into thin, almost thin slices. Set aside the slices, even those that are broken.
Compose the pie in the mold. Place a generous flake of butter on the bottom of the cocotte, then form a thin layer of potatoes, add a spoonful of béchamel sauce, sliced truffle, a sprinkling of Parmigiano, and cover with more potatoes. Fill the mold, leaving about 1 cm from the edge. On top of the last layer, spread a spoonful of béchamel sauce, add a knob of butter, more truffle, little Parmesan.
If the molds do not have lids, create one with aluminum foil. Bake the covered potato cakes in the preheated oven for 20 minutes.
Remove from oven and let cool for 4 minutes before serving.