Add pitted Medjool dates to work bowl of food processor.
Pulse several times to chop up and then let run on continuous speed to turn into a coarse paste, about 60 seconds.
Add peanut butter and process for another 30 seconds, or until combined. Add egg and process for another 30 seconds, or until combined. Scrape mixture off sides and back into work bowl.
Add flour, protein powder, cocoa powder and flax seeds and pulse in 15 second increments, until combined, scraping bowl down as needed. Mixture in bowl will be moist, but crumbly. If too moist (because of nut butter choice or fluctuation in egg size), just pulse in another tablespoon or two of flour.
Remove blade from bowl and use spoon or hands to pull together mixture and pack into a large dough ball. Refrigerate covered dough ball for 30 minutes.
Remove from refrigerator and use knife to cut ball in half, and then cut each half into 8 wedges (for total of 16 pieces). Use hands to form dough wedge into small ball. Use back of drinking glass or measuring cup to flatten out each ball into 1/3” circle on lightly sprayed (or use silicone liner) baking sheet. If desired, use tines of fork to make a hatch-mark design on top of each cookie.
Bake for approximately 12 minutes, remove and let cool on baking sheet for extra crispness. Store leftovers in airtight container on counter.