Mix sugar and ground nuts together. Cut butter into flour like a pie crust. Beat sour cream and yolks together, then add to flour mixture. Mix well. Divide dough into 10-12 balls and wrap in waxed paper or Handiwrap and refrigerate overnight. Roll dough thin on floured board. Brush with beaten whites and sprinkle with sugar and nuts. Cut into 16 wedge-shaped pieces and roll each piece up. Bake at 350 degrees on ungreased sheet pan for 15-20 minutes.