Divide the dough into two parts.
Add cocoa and sour cream to one of them.
Knead the chocolate dough.
Both types of dough are wrapped in plastic wrap and sent to the refrigerator for half an hour.
Divide each dough into 4 parts.
Roll out each part of the dough into a thin rectangle measuring 9 * 15 cm, about 2 mm thick. Trim the edges evenly, leave the trimmings.
Now we spread the white and chocolate dough alternately on top of each other, sprinkling each layer of dough with coarsely chopped nuts.
From the saved scraps, too, to form layers.
Sprinkle the last layer of dough with walnuts.
Wrap everything in parchment paper and roll out a little with a rolling pin, pressing the layers. We send it to the freezer for 30 minutes.
Then remove the parchment and cut the dough into pieces 1-1. 5 cm thick.
Place on a baking sheet lined with parchment and bake in a preheated 170 degree oven for 15-20 minutes.