Mix flour and butter for pastry. Add sugar, salt and beaten egg yolks. Add sour cream. Knead until smooth. Form 60 balls. Chill overnight.
Roll each ball thin. Fill at base, roll and seal.
Filling: Beat egg whites and add sugar and beat until stiff. Add flavoring and nuts. Place filling into dough and roll. Bake at 350F for 20 minutes or until slightly brown. Sprinkle with powdered sugar.