Process 1 cup + 3 tablespoons (140g) flour, ¾ cup pistachios (reserve remaining ¼ cup), ½ cup (100g) sugar, ¼ cup (36g) cornstarch, ½ teaspoon salt, ¼ teaspoon cardamom and ¼ teaspoon nutmeg in a food processor until pistachios are finely ground, about 40 seconds, stopping to stir halfway through.
Add remaining ¼ cup pistachios, ½ cup (113g) butter and ½ teaspoon vanilla bean paste to food processor; process until a dough comes together, pulsing as needed, 20–30 seconds.
Turn dough out onto a sheet of plastic wrap and firmly press together then roll into a 1½×12-inch log. Tightly wrap with plastic and refrigerate for 2 hours or up to 1 week.
Preheat oven to 325°F (163ºC) with racks set in upper-middle and lower-middle positions. Line 2 baking sheets with parchment paper.
If using sparkling sugar, pour sugar into a small tray. Unwrap chilled dough and let sit 5 minutes to slightly soften. Roll dough log through sugar, lightly pressing down to secure sugar. Keep rolling and pressing until log is completely covered. (If not using sparkling sugar, move on to step 6.)
Slice chilled dough into ¼-inch thick slices and transfer to prepared baking sheets, spacing 1-inch apart.
Bake until edges begin to brown and cookies are set, 30–35 minutes, rotating pans front to back and up to down, halfway through. Cool cookies on sheet pans 5 minutes, then transfer to wire rack to cool completely.
If using white chocolate, melt chocolate chips in a microwave-safe bowl on 50% power in 30 second increments until melted. Drizzle over cooled cookies and sprinkle with white sparkling sugar, if using.
Let chocolate set, then store in an airtight container at room temperature for up to 2 weeks.