Stir flour, baking powder, and salt together in a mixing bowl.. Cut in butter. Dissolve yeast in water, stir in egg yolks, sour cream and vanilla. Blend into flour mixture. Refrigerate 1 hour.
Heat oven to 400 degrees. Beat egg whites until foamy; gradually add sugar; beat until stiff. Fold in nuts and almond extract.
Divide dough into 4 parts. Roll each part into a 9 inch circle on a board sprinkled with powdered sugar. Cut each circle in 12 wedges. Spread 1 heaping teaspoonful meringue on each. Roll, beginning at the wide end. Bake on lightly greased baking sheet 10 to 12 minutes or until golden brown. Sprinkle with powdered sugar.