How to Make It
Preheat oven to 350°.
Weigh or lightly spoon flours and cornstarch into dry measuring cups; level with a knife. Combine flours, cornstarch, cocoa, and next 5 ingredients (through salt) in a medium bowl; stir with a whisk.
Beat brown sugar, granulated sugar, coffee granules, vanilla, and eggs with a stand mixer at medium speed until well blended. Gradually add flour mixture; beat until blended. Add pistachios; beat on low until blended.
Turn dough out onto a lightly floured surface; divide dough in half. Shape each half of dough into a 12-inch-long roll on a baking sheet lined with parchment paper; pat to a 3/4-inch thickness. (Flour hands with brown rice flour if dough is sticky.)
Bake at 350° for 20 minutes or until firm to touch. Remove rolls from baking sheets; cool 30 minutes on a wire rack. Cut each roll diagonally into 20 (1/2-inch) slices Place slices on baking sheets, and bake at 350° for 6 to 8 minutes. Turn slices over and bake an additional 6 to 8 minutes (cookies will be slightly soft in center but will harden as they cool). Remove from baking sheets; cool completely on wire rack.
To shave 6 to 8 minutes off your baking time, place the sliced biscotti straight up on the baking sheet with cut edges exposed for the second bake. This allows both sides to brown evenly without having to flip them.