Prep the pistachios: Pulse pistachios in a food processor until finely chopped—about the size of coarse sand. Avoid over-processing into a paste.
Cream the butter and sugar: In a large bowl, beat softened butter and 1/2 cup powdered sugar until smooth and fluffy, 1–2 minutes. Mix in vanilla (and zest if using).
Add dry ingredients: Sprinkle in salt, then add flour on low speed until just combined.
Fold in pistachios. The dough should be soft but not sticky.
Chill the dough: Cover and refrigerate for 45–60 minutes. This helps prevent spreading and boosts tenderness.
Preheat and portion: Heat oven to 350°F (175°C).
Line two baking sheets with parchment. Scoop 1-tablespoon portions and roll into smooth balls. Space about 2 inches apart.
Bake: Bake 12–14 minutes, until the bottoms are lightly golden and tops look set.
They should not brown deeply.
First sugar roll: Let cookies cool on the sheet for 3–4 minutes, then gently roll warm cookies in powdered sugar. Place on a rack to cool completely.
Second sugar roll: Once fully cool, roll again in fresh powdered sugar for a snowy, even coat.