Put the rye and wheat groats in a large enough bowl. Pour the boiling water over them.
Add the honey, oil and salt and stir. Then let the mixture rest at room temperature with the lid closed for about 36 hours.
Then gradually knead the flour into the dough with the dough hooks of the hand mixer or food processor.
Oil a 28 to 30 cm loaf pan.
Shape the dough into a loaf with floured hands, place in the pan. Press firmly to eliminate air bubbles and cracks.
Cover with a dishcloth and let the bread rest for about 3 hours.
Preheat the oven to 150 °C. Place an ovenproof dish with boiling water on the bottom of the oven.
Brush the bread with water and bake on the lowest rack in the oven for about 4 hours. Brush with water several times.
Remove the bread from the pan, wrap it tightly in a dishcloth and then in a thick woolen blanket. Mature for about 12 hours.