Sift flour and salt in a large bowl. Cut in butter with pastry blender of two knives as for a pie crust, until crumbly. Dissolve yeast in warm water, and mix in egg yolks, vanilla and almond extracts and sour cream. With a wooden spoon, stir wet ingredients into flour mixture until well blended. Cover and chill at least 2 hours, preferably overnight.

To make filling: beat egg whites until foamy. Gradually add ¾ cup sugar and beat until stiff. Gently fold in vanilla and almond extracts, and nuts.

When ready to bake, preheat over to 375°. Divide dough into 6 parts. Sift powdered sugar over a clean surface and roll each piece of dough into a circle about 9-inches in diameter. Cut into 8 wedges. Spread each wedge with approximately 1 teaspoon of filling, leaving a nice border. Roll up beginning at widest point. Place pointed edge down on a greased cookie sheet and shape into crescents.

Bake 15-20 minutes. Remove from sheer immediately and sift with powdered sugar while still warm. (Dot sugars again, heavily, once cookies cool.)