Put the flour into a large bowl and make a well. Put the yeast into the well and add 100 ml water. Cover and allow to rest for 15 min.
Add the rest of the ingredients and mix until forming a dough. Move it on a hard floured board and kneed for about 10 min.
Put the dough on the hard board and incorporate the mashed potatoes.
It will become very hard to mix, very gooey, but do not add any more flour. Pop back in the bowl, cover again and allow to rest for 1 - 2 hours.
Put the dough onto a floured surface. Divide it in 4 equal portions. Flour your hands and try to form a ball. Place it on a baking tray, flour the top, cover and rest for 1 hour.
Preheat the oven at 200° C.
Bake for 45 min. Remove from the oven and rest before cutting.
