Sift flour, and salt. Sprinkle yeast over flour. Cut in margarine. Make a well and pour in beaten egg yolks, sour cream and vanilla. Knead until smooth. Refrigerate at least one hour. For filling, beat egg whites until stiff. Fold in sugar, nuts, and vanilla. Set aside. Remove dough from refrigerator, form into ball, and flatten until it resembles a thick pizza crust. Cut into 8 triangles. Roll each triangle into size of 10 inch pie crust; cut into 8 triangles. Place 1/2 to 1 teaspoon filling at wide end, and roll into crescents, pinching ends under. Bake at 375F on ungreased cookie sheets for 15-18 minutes.