Prepare dry ingredients: Using a food processor or a pastry blender, blend the butter into the flour, creating a coarse, crumb-like consistency.

Prepare wet ingredients: Mix the egg yolks and sour cream in a large bowl.

Make the Dough: Add the flour mixture to the egg mixture. Blend and knead lightly until the consistency is like a pie dough. Shape into small, walnut-sized balls, cover, and refrigerate for at least an hour.

Meanwhile, beat the egg whites until fluffy. Add ⅓ of the sugar at a time and beat until well blended and the mixture is stiff.

Gently fold in the ground nuts.

Coat the dough balls: Whisk together two tablespoons of all-purpose flour and two tablespoons of sugar in a medium bowl. Take half of the dough balls out of the refrigerator and roll them into the flour/sugar mixture. Keep the rest chilled.

Roll the dough: Roll the balls out on a small amount of flour/sugar mixture into a thin circle.

Fill the dough: Place a heaping teaspoon of filling on each dough circle and roll it up into a crescent shape. Pinch the ends tightly - place seam-side down on a parchment paper-lined or greased cookie sheet.

Repeat the above steps with the rest of the dough and filling.

Bake the cookies: Bake kiflies in an oven at 350 degrees Fahrenheit for 12 to 15 minutes. Cool slightly.

Coat the cookies: Roll the warm cookies in a bowl of confectioners' (powdered) sugar.