Wash the wheat and rye berries in plenty of water, then place in a big pan and cover with double their volume of water and let soak overnight.
The next morning, remove the water, and spread the soaked berries on a large baking tray. Place in a warm place and make sure you keep them moist by spraying them with water and tossing them at least two-three times a day. At the end of the second day or at the beginning of the third, the sprouts should be ready.
Preheat the oven to 165 °C/329°F.
Transfer the sprouts into the food processor, add the salt and process to obtain a wet dough.
Line a baking sheet with parchment paper, and use your hands to create little buns, or any other bread shape you prefer.
Top with nigella seeds, and bake in the oven for 30 minutes.
When ready, remove from the oven, and let cool completely before eating.