Instructions: In a bowl of a food processor fitted with a metal blade, grind pistachios until fine but not powdery. Divide ground pistachios equally between the sanding sugar and flour; set aside.

In the bowl of an electric mixer fitted with the paddle attachment, cream the butter and sugar on medium speed until fluffy, 3 to 4 minutes. Add vanilla and salt, and beat for 1 minute. Add the yolks one at a time, and beat until evenly combined. Add the flour and pistachio mixture, and mix until just combined. Remove the dough, and form into a 4- by 6-inch rectangle; wrap in plastic, and chill for 1 hour.

Heat oven to 350 degrees. Line two baking sheets with Silpats, and set aside. On a lightly floured surface, roll out the dough to a 1/8-inch thickness. Brush the dough with the egg white to moisten. Cover evenly with the pistachio-sanding sugar mixture. Lightly press the mixture into the dough with the rolling pin. Using a 1 1/2-inch fluted square cookie cutter, cut cookies as close as possible to avoid waste. Place on prepared baking sheets.

Bake until the edges are just lightly golden, about 18 minutes. Transfer cookies to a cooling rack. Store in an airtight container for up to 1 week.

This recipe yields about 48 cookies.

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