In a large bowl, combine the cold, diced butter with powdered sugar. Beat with an electric mixer until smooth and creamy, frequently scraping down the bowl to ensure all ingredients are fully incorporated.
1 cup (227g) salted butter, ½ cup (60g) powdered sugar
Add the vanilla extract and salt to the butter mixture. Gradually add the flour and incorporate it with a spatula just until the dough starts to come together. Avoid overmixing.
1 teaspoon pure vanilla extract, ¼ teaspoon salt, 2 cups (282g) all-purpose flour
Fold in the chopped pistachios and white chocolate. Divide the dough into two equal portions, shaping each into a log about 6 ½ inches long and 1 ½ to 1 ¾ inches in diameter. Press firmly to eliminate air pockets and ensure an even texture. On a lightly floured surface, roll each log to refine the shape.
½ cup chopped pistachios, ½ cup chopped white chocolate
Wrap each log tightly in plastic wrap or parchment paper and refrigerate for at least 1 hour or until the dough is well chilled.
Preheat the oven to 350°F. Remove the dough logs from the refrigerator. Slice each log into 14–15 pieces, each less than ½-inch thick, and arrange them on a parchment-lined baking sheet. Bake for 8–10 minutes or until the edges are lightly golden. If the cookies have softened during this time, refrigerate them for 15-20 minutes, so they’re hard just before baking. This will prevent them from losing their shape.
After baking, let the cookies cool completely on a wire rack.