Heat oven to 325°F. Line two baking sheets with parchment.
Cream butter and powdered sugar until smooth and slightly fluffy, about 2–3 minutes.
Mix in vanilla, orange zest, and salt until combined.
Whisk flour and cornstarch together. Add to the bowl and mix on low just until a soft dough forms.
Fold in chopped pistachios evenly, avoiding overmixing.
Divide dough in half. Shape each into a 1.5-inch-thick log, wrap, and chill 20 minutes.
Slice logs into 1/4-inch rounds. Roll edges in turbinado sugar if using.
Arrange on sheets, spacing 2 inches apart. Bake 12–14 minutes until set with lightly golden bottoms.
Cool 5 minutes on the pan, then transfer to a rack to cool completely.