Preheat the oven to 350 degrees F. Line two baking sheets with parchment paper.
For the cookies: In a high-powered food processor, blend the pistachios and almonds until spreadable, 10 to 15 minutes. Remove 1/4 cup (64g) of the mixture and set aside for the filling. To the food processor, add the salt, lemon zest, almond extract and granulated sugar and blend together. Add the egg and blend to combine. Scoop out 16 tablespoon-size balls and roll in granulated sugar. Flatten, place on a baking sheet 1 inch apart and bake for 12 minutes (they'll still be very soft but they'll firm up as they cool). Let cool on the pans for 10 minutes and then transfer to a wire rack to cool completely.
For the filling: In a stand mixer fitted with a paddle attachment, blend together the butter and reserved pistachio-almond butter. Add the powdered sugar and blend to combine. Add the salt, vanilla extract, almond extract and lemon zest. Fill a piping bag with the filling and pipe in the centers of half of the cooled cookies. Sandwich them with the other half of the cookies and then roll in sprinkles. Enjoy!