For dough: Dissolve yeast in warm water. Sift flour; add salt. Add butter, eggs yolks, sour cream.
, vanilla and dissolved yeast mixture to flour mixture; work with hands until a moist dough forms. Cover and refrigerate 1 to 2 hours, or overnight.
Divide dough into eight pieces. Dust rolling pin and work surfaces with powdered sugar. Working with one piece of dough at a time, roll out dough to about 1/8 inch thickness (slightly thinner than pie dough, more like noodle dough).
Cut dough into a circle approximately 8 inches in diameter. (You may want to use a stainless steel bowl and just press out a circle). Refrigerate dough circle. Continue rolling and cutting remaining dough, refrigerating circles as you go. Re-roll leftover dough pieces and cut into circles.
Cut each circle of dough into 16 triangular pieces or wedges.
For filling: Beat egg whites until foamy. Gradually add sugar; beat until stiff. Fold in pecans and vanilla.
Spread 1/2 teaspoon filling on each triangle of dough; roll up, beginning with largest end. Place roll, small end down, on greased cookie sheet.
Bake in a 350 degrees F oven 10 to 12 minutes, or until slightly browned on bottom. Immediately transfer to racks to cool.
Sift powdered sugar over cooled cookies. Store in airtight container. Yield: About 10 dozen cookies.