01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a large bowl, beat softened butter and powdered sugar until light and fluffy. Add egg yolk and vanilla extract; mix thoroughly.
03 - Sift in all-purpose flour and salt. Incorporate until a soft dough forms.
04 - Roll dough into 1-inch balls and arrange on prepared baking sheets, spacing them 2 inches apart. Gently flatten each ball using your palm or the back of a glass.
05 - Bake for 10 to 12 minutes or until edges are turning golden. Allow cookies to cool completely on a wire rack.
06 - Pulse shelled pistachios and granulated sugar in a food processor until finely ground. Add melted white chocolate, softened butter, and 2 tablespoons heavy cream; blend until smooth. If needed, add an additional tablespoon of cream for a spreadable consistency.
07 - Spread pistachio cream on the flat side of half the cookies. Top with remaining cookies to create sandwiches.
08 - Roll edges of filled cookies in finely chopped pistachios.
09 - Store assembled cookies in an airtight container at room temperature for up to 3 days.