Prepare the potatoes as jacket potatoes.
In a bowl, mix water with yeast. Mix spelt, rye, anise, fennel seeds and caraway seeds in a bowl and grind finely. Put the flour in a bowl and press a well in the center.
Pour in the yeast water and mix with a little flour from the edge of the well.
Cover the dough and let it rise for about 20 minutes. In the meantime, peel the potatoes.
Press them through a press or mash them very finely with a fork. Add to the dough together with the salt.
Melt the butter and knead into the dough. Knead the dough thoroughly. Cover and let rise again for about 30-40 minutes. Knead the dough again and shape into an oblong loaf. Place on a baking tray lined with baking paper and let rise again for 15 minutes. In the meantime, preheat the oven to 220° C.
Beat the egg and brush the bread with it. Sprinkle with the sesame seeds. Cut the loaf lengthwise 1/2 cm deep. Place in hot oven and bake for 10 minutes, then turn down to 200° C and bake for another 25-30 minutes.