Meringue Shell Cookies (Rakushki)

Bahan-bahan (60 porsi)

• 1 cup unsalted butter, softened ((16 Tbsp or 226 grams))
• 1/2 cup sour cream
• 3 egg yolks (room temperature)
• 2 1/2 cups all-purpose flour (315 grams *measured correctly)
• 3 egg whites (room temperature)
• 3/4 cup granulated sugar
• 1 1/2 cups walnut pieces (3 pieces per cookie)