In a large bowl, combine flour and salt; cut in butter until mixture resembles coarse crumbs. In a small bowl, whisk the egg yolk, sour cream and vanilla; add to crumb mixture and mix well. Cover and refrigerate for 4 hours or overnight.
Divide dough into thirds. On a lightly floured surface, roll each portion into a 10-in. circle. Combine the apple, walnuts, raisins, sugar and cinnamon; sprinkle 1/2 cup over each circle. Cut each circle into 12 wedges.
Roll up each wedge from the wide end and place point side down 1 in. apart on greased baking sheets. Curve ends to form crescents. Whisk egg white until foamy; brush over crescents.
Bake at 350° for 18-20 minutes or until lightly browned. Remove to wire racks to cool. Store in an airtight container.