Directions

1. Heat sour cream and water until warm (100° to 110°F). Sprinkle in yeast; stir until dissolved.
2. Combine butter and 1/2 cup flour in a large mixer bowl. Add sour cream mixture and beat 1 minute at low speed of electric mixer, scraping bowl occasionally. Add egg yolks and 1/4 cup flour; beat 1 minute at medium speed, scraping bowl occasionally. Stir in enough remaining flour to make a soft dough. Knead on lightly floured surface 8 to 10 minutes; dough will not be smooth. Divide dough into 3 equal pieces; cover tightly with plastic wrap. Refrigerate 2 to 24 hours.
3. For Nut Filling: Beat egg whites in a medium bowl until stiff peaks form. Combine walnuts, sugar and vanilla. Fold into beaten egg whites.
4. On a surface dusted with powdered sugar, roll each piece of dough to a 10-inch circle. Cut each into 8 wedges. Top wide edge of each wedge with about 1 tablespoon Nut Filling. Roll up from wide end to point. Place on greased baking sheets, with points underneath. Brush with melted butter.
5. Bake in preheated 375°F oven for 18 to 20 minutes or until golden brown. Remove from baking sheets; cool on wire racks. Sprinkle with powdered sugar while warm, if desired.