In the bowl of a stand mixer fitted with the paddle attachment, beat the butter for 1 minute until smooth. Add the confectioners' sugar, vanilla bean seeds, salt and vanilla to the butter and blend on medium low until combined.
Add the flour a little at a time and mix until incorporated.
Fold in the pistachios using a rubber spatula.
Place the dough on a large piece of parchment paper lightly dusted with flour. Form the dough into a log 12-inches long and about 1½ inches thick. Wrap the dough tightly in the parchment paper and refrigerate for at least 1 hour or overnight.
When ready to bake preheat oven to 350 degrees.
Remove the dough from the refrigerator to rest while preparing the egg wash.
Gently beat one egg white with 1/2 teaspoon water.
Lightly brush the entire log with the egg white then roll in the coarse sugar to coat.
Slice into ½-inch thick rounds and place on a parchment lined baking sheet.
Bake for 16 to 20 minutes or until lightly browned on the bottom and set.
Cool on a wire rack and store in an airtight container.