Cook the potatoes the day before. Peel the potatoes, put them through a potato press. Mix the pressed potatoes with the potato flour and eggs well until you get an even dough. Shape into a large roll and cut into slices.
Dice the bacon and fry in a pan with the diced onion until the diced bacon is lightly crispy.
Roll out the dough slices so that they are approx. 1 - 2 cm thick and the size of a dessert plate. Pour the diced ham mixture in the middle and roll up the pastry plates. If there is still a bit open at the top, simply seal it with dough. Do that with the whole dough. Put in a roasting pan greased with crackling lard. Place in the oven at 200 degrees for 45 minutes. Brush with crackling lard again and again during baking so that everything becomes really crispy.