1For Filling: Beat egg whites and sugar until smooth. Add walnuts. Chill until firm.
2For Dough: Mix flour and butter like pastry. Add beaten yolks and sour cream. After mixing, knead dough. Refrigerate until firm.
3Generously flour table or board when rolling dough. Form dough into small balls and roll out paper thin. Take a teaspoon of filling and place on dough. Fold into a crescent shape.
4Bake @ 350 on parchment paper until golden brown (about 18-20 min). After cooling, dust with powdered sugar.