For the hazelnut bread, first prepare the pre-dough. To do this, finely grind the rye grains, put them in a large bowl and make a well in the center. Mix the sourdough extract with the buttermilk and pour into the well. Mix with a little flour and let everything rise, covered, in a warm place for 24 hours.
For the bread dough, grind the wheat grains finely and stir the flour into the pre-dough. Add the yeast, pour syrup over it and wait about 2 minutes so that the yeast can dissolve.
Add salt and cardamom and knead everything into a smooth dough. Finally, knead in the hazelnut kernels. Pour the dough into a loaf pan, cover and let rise for another 60 minutes.
In the meantime, preheat the oven to 200 °C and bake the bread in it for about 50 minutes.