Make dough. For this the flour, put the chopped butter and RUB with your hands into fine crumbs. Add the brown sugar from "Mistral" and the yolks, quickly knead the dough.

Divided into two parts. One to leave without change, just roll up into a ball. In other to put the sour cream and cocoa. Knead until smooth and roll into a ball. Remove in the cold for one hour.

Then divide each ball into four parts. Roll out one bright piece into a rectangle on a flour covered table. Transfer on baking paper, large size. Lay the pieces of walnut in the distance. Roll out one dark part and using a rolling pin to cover with a light rectangle. Put it on nuts in between the first. Don't worry, You'll feel when you put.

So layer by layer to make all the pieces. Then trim around the edges, forming a rectangle. To assemble trim, crease and roll. This is the top layer, which is not necessary to put walnuts. Trim. Cover with paper and rolled the top with a rolling pin, pressing the layers together, without breaking the rectangle.

Remove paper and cut into slices thick 1 cm, Put on a baking tray lined with paper.

Bake at t=170 for about 20 min. Take out and allow to cool without removing.