Preparation

• Place the pistachios and sugar in a food processor. Process until the nuts are very finely ground but not pasty, 30 to 60 seconds.
• With the motor running, pour in the egg whites and almond extract. Process until the mixture balls up around the blade and then relaxes into a thick, sticky paste, about 30 seconds. It should be thick enough to scoop with a spoon.
• Line two large baking sheets with parchment, and coat the parchment with cooking spray.
• Using 2 teaspoons, drop heaping spoonfuls of the paste in mounds onto the baking sheets (about 2 teaspoons per mound), leaving 2 inches of space between (about 16 per baking sheet). Smooth and round out the tops with lightly moistened fingers, but don’t press down or flatten the mounds. Let sit, uncovered, for 1 hour.
• Meanwhile, position a rack in the center of the oven and heat the oven to 300°F.
• Bake the amaretti, one sheet at a time, until they are just set on top and beginning to color, 15 to 20 minutes. Transfer the baking sheets to cooling racks and let cool completely.
• Dust lightly with confectioners’ sugar. The amaretti will keep for 1 week in an airtight container at room temperature.