Place flour in a large bowl; cut in butter until mixture resembles coarse crumbs. In a small bowl, whisk the sour cream, egg yolks and vanilla; add to crumb mixture and mix until dough forms a ball. Cover and refrigerate for 4 hours or overnight.
Divide dough into fourths. On a lightly floured surface, roll each portion into a 10-in. circle.
Whisk egg whites and water; brush over dough. Combine sugar and cinnamon; set aside 1/4 cup in a small bowl. Sprinkle remaining cinnamon-sugar over the dough. Cut each circle into eight wedges.
Roll up each wedge from the wide end; roll in reserved cinnamon-sugar. Place point side down 1 in. apart on greased baking sheets. Curve ends to form crescents.
Bake at 375° for 15-17 minutes or until lightly browned. Remove to wire racks to cool. Store in an airtight container.