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1
Heat the oven to 325 degrees F and arrange a rack in the middle.
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2
Cut a 22-inch-long piece of parchment paper and fold over the edges so it measures 8 inches wide; set it aside.
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3
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).
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4
Be sure to fit the parchment as smoothly as possible into the pan, snugly creasing it into the corners.
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5
Coat the bottom of the parchment with more butter and set the pan aside.
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6
Place 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.
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7
Remove them from the pan and allow to cool for 10 minutes.
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8
Combine 1/2 cup of the pistachios, 1/2 cup of the sugar, and the salt in a food processor.
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9
Process until the pistachios are ground and the mixture resembles coarse sand, about 30 seconds.
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10
Add the flour and pulse to combine, about 10 (1-second) pulses.
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11
Add the measured butter and lemon zest and pulse again until the dough is just blended and comes together, about 10 (1-second) pulses.
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12
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.
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13
Pour the mixture into the prepared pan and, using the base of a measuring cup or a glass, press it evenly into the pan.
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14
Use a fork to prick the shortbread gently all over the surface.
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15
Sprinkle the top of the shortbread evenly with the remaining 2 teaspoons of sugar.
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16
Bake until light golden brown, about 35 to 40 minutes.
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17
Transfer the pan to a wire rack and allow the shortbread to cool for 15 minutes.
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18
To remove, grip the parchment hanging over the edges and pull the shortbread out of the pan.
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19
Transfer it to a cutting board and remove and discard the parchment.
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20
Using a serrated knife, cut the warm shortbread into 1-by-2-inch rectangles.
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21
Allow to cool completely before serving, about 10 minutes.
