PISTACHIO SHORTBREAD

Steps:

• In the bowl of a food processor, grind pistachios until fine but not powdery. Divide ground pistachios equally between sanding sugar and flour; set aside.
• In the bowl of an electric mixer fitted with the paddle attachment, cream butter and sugar on medium speed until fluffy, 3 to 4 minutes. Add vanilla and salt, and beat for 1 minute. Add yolks one at a time, and beat until evenly combined. Add flour and pistachio mixture, and mix until just combined. Remove dough, and form into a 4-by-6-inch rectangle; wrap in plastic, and chill for 1 hour.
• Preheat oven to 350 degrees. Line two baking sheets with Silpats (French nonstick baking mats) or parchment paper, and set aside. On a lightly floured surface, roll out dough to a 1/8-inch thickness. Brush dough with the egg white to moisten. Cover evenly with pistachio-sanding-sugar mixture. Lightly press mixture into 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 edges are just lightly golden, about 18 minutes. Transfer cookies to a cooling rack. Store in an airtight container for up to 1 week.