8 tablespoons cold unsalted butter (1 stick), cut into small pieces, plus more for coating the pan and parchment
1 teaspoon finely grated lemon zest (from about 1 medium lemon)
Shortbread is one of the easiest sweet treats to make. This recipe requires only a few ingredients and a minimal amount of time to get rich, buttery cookies flecked with bright green pistachios and lemon zest. To keep the cookies from sticking to the pan and crumbling, make a sling out of parchment paper to easily remove the shortbread from the pan.
1Heat the oven to 325°F and arrange a rack in the middle.
2Cut a 22-inch-long piece of parchment paper and fold over the edges so it measures 8 inches wide; set it aside. Coat an 8-by-8-inch metal baking pan with butter and line it seam-side down with the parchment (the 2 long ends will hang over the edges). Be sure to fit the parchment as smoothly as possible into the pan, snugly creasing it into the corners. Coat the bottom of the parchment with more butter and set the pan aside.
3Place the pistachios in a large frying pan over medium heat and toast, stirring occasionally, until they are aromatic and slightly golden, about 10 to 15 minutes. Remove them from the pan and allow to cool for 10 minutes.
4Combine 1/2 cup of the pistachios, 1/2 cup of the sugar, and the salt in a food processor. Process until the pistachios are ground and the mixture resembles coarse sand, about 30 seconds. Add the flour and pulse to combine, about 10 (1-second) pulses. Add the measured butter and lemon zest and pulse again until the dough is just blended and comes together, about 10 (1-second) pulses. Add the remaining 1/4 cup of whole pistachios and pulse until they are broken up into pieces about the size of peppercorns, about 10 (1-second) pulses.
5Pour the mixture into the prepared pan and, using the base of a measuring cup or a glass, press it evenly into the pan. Use a fork to prick the shortbread gently all over the surface. Sprinkle the top of the shortbread evenly with the remaining 2 teaspoons of sugar. Bake until light golden brown, about 35 to 40 minutes.
6Transfer the pan to a wire rack and allow the shortbread to cool for 15 minutes. To remove, grip the parchment hanging over the edges and pull the shortbread out of the pan. Transfer it to a cutting board and remove and discard the parchment. Using a serrated knife, cut the warm shortbread into 1-by-2-inch rectangles. Allow to cool completely before serving, about 10 minutes.