Sprinkle yeast over warm water. Add 1 teaspoon sugar. Let stand 10 minutes or until yeast is softened. Sift together flour and salt. Cut in butter until mixture resembles coarse meal. Blend in egg yolks and softened yeast. Mix until a smooth ball is formed.
Beat egg whites until stiff but not dry. Gradually beat in the 1/2 cup sugar. Continue beating until stiff and peaked. Fold in vanilla.
Divide dough in half. Roll out each half on a lightly floured surface into a 9x13-inch rectangle. Spread with egg white mixture and sprinkle with nuts. Roll up as for a jelly roll. Place on grease baking sheet.
Make a 1/2-inch-deep cut lengthwise down center of each roll. Bake immediately (no rising) at 375 for 22 minutes. When warm, sprinkle with powdered sugar. Cool thoroughly. Slice diagonally.
Bake