In a standing mixer fitted with a paddle attachment, or using a hand mixer, cream together the butter and sugar until light and fluffy, about 3 – 5 minutes. Add the vanilla and beat again until combined. With the mixer on medium, gradually add the flour, followed by the salt, and beat until evenly incorporated. Using a spatula or wooden spoon, stir in the pistachios. Shape the dough into a flat disk and wrap in plastic wrap. Transfer to the refrigerator to chill overnight.
Preheat the oven to 325˚F. Line 2 baking sheets with parchment paper or silicone mats.
Roll the chilled dough into 1-inch balls and place 1-inch apart on the prepared baking sheets. Transfer to the oven and bake until the cookies are golden on the bottom and just starting to color around the edges, about 15 – 17 minutes. Remove from the oven and allow the cookies to cool on the baking sheets for 5 minutes.
After they have cooled slightly, dust the cookies with confectioners’ sugar, and transfer to a wire rack to cool completely before serving.
Store cookies in an airtight container.