STEP 1

Whisk together both flours, both starches, and salt in a bowl; set aside. Combine butter, sugar, and vanilla seeds in another bowl and beat on medium speed of hand mixer until smooth and evenly combined. Add dry ingredients and pistachios, and beat until smooth. Transfer half the dough to a sheet of parchment paper and roll into a 2 ½"-wide cylinder; repeat with remaining half of dough. Refrigerate until firm, about 1 hour.

STEP 2

Heat oven to 350°. Unwrap cylinders and cut into ¼"-thick slices; transfer to parchment paper-lined baking sheets and bake until lightly golden, about 10 minutes.