01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a large bowl, use a mixer to combine softened butter with powdered sugar until the mixture becomes light and fluffy. Incorporate egg yolk and vanilla extract, mixing until fully blended.
03 - Sift in all-purpose flour and salt. Mix until a soft dough forms and no streaks of flour remain.
04 - Portion dough and roll into 1-inch balls. Arrange balls on prepared baking sheets with 2 inches of space between. Flatten each ball slightly with your palm or a glass.
05 - Bake for 10 to 12 minutes, or until edges begin to turn golden. Transfer to a wire rack to cool completely.
06 - In a food processor, pulse pistachios and granulated sugar to a fine meal. Add melted white chocolate, softened butter, and 2 tablespoons cream. Process until smooth, adding additional cream if needed for a spreadable consistency.
07 - Spread pistachio cream onto the flat side of half of the cookies. Top each with a second cookie to create a sandwich.
08 - Roll the edges of filled cookies in finely chopped pistachios for garnish.
09 - Store assembled cookies in an airtight container at room temperature for up to 3 days.