Mix butter, flour, egg yolk and sour cream in a bowl. Wrap in waxed paper and chill for at least 2 hours until firm.

Combine raisins, sugar, cinnamon, and nuts in a bowl. Set aside.

Cut dough into 4 equal parts. Working with one piece of dough at a time, on a floured surface, roll out to about a 1/8” thick rectangle and sprinkle liberally with the raisin mixture. Roll into a log.

Repeat with the other 3 pieces of dough. Put them on a parchment-lined baking pan and refrigerate for about 15 minutes to firm them up for slicing.

Brush each log with egg white and cut each into 10-12 equal pieces.

Bake at 375° for 20-25 minutes, or until golden brown.