Step 1

Add the flour to a large bowl. Using a pastry cutter, two knives or your fingers, cut the butter into the flour, until it resembles even-sized crumbs. Add in the sour cream and egg yolk. Mix until the dough comes together in large clumps.

Step 2

Form the dough into three equal sized balls. Pat each into a disc and then wrap tightly with plastic wrap.

Step 3

Transfer to the refrigerator and let chill at least 2 hours or even overnight, until well chilled. You want it to be firm enough so that you can roll it out easily.

Step 4

Preheat the oven to 350ºF. Line a large baking sheet with parchment paper and set aside.

Step 5

In a medium bowl, mix together the walnuts and brown sugar until well combined, making sure to break up any clumps of brown sugar. Set aside.

Step 6

Working one ball of dough at a time (keep the other balls in the fridge while you do this), place the chilled dough on a well-floured work surface (I like to do this on well-floured parchment paper). Roll out into a circle that is between ⅛ and ¼ inch in thickness.

Step 7

Sprinkle ⅓ of the walnut / sugar mixture evenly over the dough (all the way to the edges) then press down lightly into the dough. With a pastry or pizza cutter, slice the dough like you would a pizza, into 16 equal triangles.

Step 8

Starting with the wide end, roll up each triangle - some of the filling will fall out - that’s totally fine. Place the shaped cookies on the prepared baking sheet, with the seam side / tip down. Repeat this process with the remaining two balls of dough.

Step 9

Bake for about 22 to 24 minutes, until golden brown. Let cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely. If baking in batches, keep any unbaked, shaped cookies in the refrigerator.

Step 10

Once completely cool, dust generously with confectioners’ sugar.