Line 2 half-sheet pans with parchment paper and set aside.
Combine 1/2 teaspoon of the salt with 1 1/2 teaspoons of the nigella seeds in a small bowl and set aside, then place the remaining salt and nigella seeds in a medium mixing bowl and whisk in the flours along with the cardamom, coriander, and black pepper.
Install the paddle attachment on the stand mixer and cream the butter and sugar at medium speed for 3-5 minutes, or until lighter in color and fluffy. Kill the motor and scrape down the sides of the bowl.
Add the flour mixture in one dose, then turn the mixer to the lowest setting and mix until a dough just comes together, about 30 seconds. Add the pistachios and mix another 10 seconds.
Deposit the dough onto a clean countertop and divide in half. Place one of the halves on a 12" x 16" piece of parchment paper and form into a 9-inch log shape. Roll snugly in the paper and twist the ends to seal. Repeat with the other half of the dough and refrigerate both packets for 1 hour. This may be done a day in advance if desired.
Place a rack in your oven's middle position and heat to 350℉. Unwrap one of the dough logs and slice into 1/2-inch rounds. Place the cookies on the prepared sheet pan, brush lightly with egg wash, and sprinkle with half the reserved salt/nigella seed mixture. When the oven reaches temp, bake for 15-17 minutes, until golden brown on the bottoms. Repeat the procedure with the second dough log.
When the cookies are cool enough to handle, transfer to a wire rack to cool thoroughly before serving. Store in an airtight container or zip-top bag for up to a week.