Wash and peel the potatoes. Using the mandoline, cut into 1/4 in thick slices.
Blanch the potato and sweet potato slices in separate saucepans of unsalted boiling water for 3 minutes. Drain.
Preheat the oven.
Brush the mold with vegan butter and arrange potato discs, overlapping. Brush each layer with melted vegan butter, season with salt and pepper and grate vegan cheese into the center each time.