Mix all the pre-fermentation ingredients in a large bowl, cover with a towel, and let it ferment at room temperature for about 10–12 hours. A foamy layer should form on top.
After fermentation add 550 g of raw buckwheat flour and salt. Mix everything together and set aside a new portion of starter.
Cover the dough again with a towel and let it rise and ferment for about 3 more hours.
After raising, optionally add pumpkin seeds, sunflower seeds, nuts, raisins or ground coriander.
Gently fold the preferable additions into the dough (it’s important not to overmix or mix too vigorously).
Pour the dough into a baking tin lined with parchment paper – the tin should be about ¾ full (this amount makes two loaves).
Preheat the oven to 200°C and let the bread rise at the same time.
Bake in the middle of the oven at 200°C for 30 minutes, then reduce the temperature to 180°C and bake for another 30 minutes.
Let it cool, then slice. Enjoy!