Blend flour and butter using pastry blender. Beat egg yolks, add sour cream and blend. Stir together yeast, sugar and water, and proof for 10 minutes. Add both mixtures to flour. Handle gently and shape to a ball (as in pie crust). Chill overnight.
To make filling, combine nuts, sugar, vanilla and beaten egg whites.
Divide into 24 balls and roll each into a circle. Cut into 8
pie-shaped pieces. Spread with filling (see recipe) and roll from outer edge to center in crescent shape. Bake on ungreased pans at 400 degrees for 15 minutes or until lightly browned
