Two Healthy Kitchens
Transfer pistachio butter to a large mixing bowl and add brown sugar, egg, and vanilla and beat on medium speed for about 3 minutes until very well incorporated, scraping the bowl once or twice.
In a medium bowl, combine flour, baking soda, and salt, stirring with a whisk to thoroughly combine. Add flour mixture to pistachio mixture and beat on medium-low just until combined.
These cookies can be made ahead. You can prepare the nut butter several days in advance, or completely make the dough a day early, and then wrap and refrigerate it until you're ready to continue.