Preheat oven to 325°F. Line cookie sheets with parchment paper.
In large bowl, beat butter and granulated sugar with electric mixer until light and fluffy. Add vanilla and mix well. Add flour, pistachios, and orange zest; mix with electric mixer on low speed until dough forms. Roll dough into 1-inch balls; place 1-in. apart on baking sheets.
Bake 19-22 minutes or until bottoms are golden brown. Remove to cooling grid; cool 5 minutes. Roll warm cookies in confectioners' sugar; cool completely.