1.
Put the white flour with the rye flour and the salt into the mixing bowl of the stand mixer, crumble in the fresh yeast and add the cold water and the apple cider vinegar. Knead the ingredients for 12 minutes until they come together into a moist, sticky dough (stand mixer: speed 1).
2.
Increase the speed by one level and knead the mixture for another 2 minutes into a soft, sticky dough (stand mixer: speed 2).
3.
Add the walnuts and mix in for about 1 minute (stand mixer: speed 1).
4.
Then cover the dough and let it rest in the mixing bowl of the stand mixer for 2 hours at room temperature.
5.
Insert the baking stone or alternatively an inverted baking sheet on the lowest rack of the oven and preheat the oven to 240 degrees top and bottom heat.
6.
Line a rectangular pan (18×25 cm) with a well-floured linen cloth and place the dough inside. Press flat to the side edge and dust again with some flour. Cover the dough and let rest for 45 minutes at room temperature.
7.
Carefully turn the dough out of the pan and cut into eight rectangular pieces. Do not press the air out of the dough. Gently place the dough pieces on a piece of baking paper and, using a dough peel, slide them into the hot oven directly onto the baking stone or the baking sheet (including the baking paper). With the oven door slightly ajar, spray plenty of warm water into the oven, close the door immediately and bake the rolls for 10 minutes.
8.
Open the oven door for 2 seconds to let the steam escape, and bake the rolls for another about 10 minutes.
9.
Let the rolls cool on a wooden board or a cooling rack after baking.