Mash the jacket potatoes (or boiled potato leftovers) with a fork or press them through the potato press. Transfer to a large bowl. Mix with the flour. Add salt and dry yeast. Add the oil to the lukewarm water and gradually knead into the flour and potato mixture with the mixer (dough hook) and work into an even dough.
Cover and let rise for at least 30 minutes.
Shape the dough into a roll on a floured worktop and divide it into 12 equal pieces. With floured hands, shape into rolls and place on a baking sheet lined with baking paper. Score in the middle with a sharp knife.
Cover the dough pieces with a clean cloth and let rise for another 30 minutes.
Place an ovenproof dish on the bottom of the oven. Preheat the oven to 190 ° C. Immediately before inserting the rolls, pour a cup of water into the tray in the oven to create steam. Slide the dough pieces onto the middle rack of the oven and bake for 40 minutes at 180 - 190 ° C top / bottom heat until crispy.