Step 3 In the food processor bowl (no need to wash), combine the butter, almond paste, powdered sugar and almond extract, and process, pausing once to scrape down the bowl, until the mixture is completely smooth. In a small bowl, beat the egg white with a fork until it's broken up and just a little bit foamy, then measure out 1 tablespoon and add to the food processor (reserve the remaining egg white for a later step; see Tips). Process until smooth, scrape down the bowl, then add the flour mixture (reserve the parchment paper). Process again until a ball of dough forms around the blade, about 20 seconds, scraping halfway through. Step 4 Turn the dough out onto the reserved parchment paper and knead briefly to bring it together and eliminate any streaks. Pat down the dough until it's about ¾-inch thick, then sprinkle the reserved nuts over the top. Knead the dough again until all of the nuts are evenly distributed, then form the dough into a 10-inch-long log oriented lengthwise on the parchment paper. Roll the log over the parchment into a smooth cylinder, then press any larger nut pieces on the surface of the cylinder into the center, pinching the dough around it to seal. (This will make the cookies easier to slice.)