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1
Pour 1/2 cup of the pistachios into a food processor and process until finely ground.
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2
With the motor running, start pouring in 1 tablespoon of the vegetable oil in a thin stream through the food processors opening, stopping when the ground pistachios turn into a paste, and adding more oil if needed.
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3
Scrape the pistachio butter into a bowl.
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4
Coarsely chop the remaining 1/4 cup of pistachios.
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5
With an electric stand mixer fitted with the paddle attachment or a hand mixer, beat the butter and brown sugar on medium speed until incorporated.
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6
Beat on high spread until very smooth, 1 to 2 minutes.
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7
On medium speed, beat in the egg yolk and vanilla until well blended, scraping down the sides of the bowl if necessary.
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8
Beat in the pistachio butter until thoroughly blended.
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9
In a medium mixing bowl, whisk together the flour and baking soda.
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10
With the electric mixer on low speed, slowly add the dry ingredients to the pistachio butter mixture until there are no patches of flour.
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11
Add the chopped pistachios and mix until thoroughly combined.
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12
Divide the dough in two.
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13
Transfer half the cookie dough to a large sheet of plastic wrap on your work surface and form it into a 7-inch log, using the plastic wrap to help roll and shape it.
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14
Wrap it in plastic wrap, twist the ends, and refrigerate for 30 minutes, or until firm.
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15
Repeat with the other half of the dough.
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16
Preheat the oven to 350F.
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17
Line a baking sheet with parchment paper, and position a rack in the middle of the oven.
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18
When the logs are firm, set them back on your work surface, and use a sharp knife to cut the dough into 1/2-inch pieces.
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19
(You should have about two dozen.)
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20
Set as many of the cookies as you intend to bake about 2 inches apart on the prepared baking sheet.
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21
Bake for 12 to 15 minutes, rotating the baking sheet front to back halfway through cooking, until they are lightly golden and the edges have started to darken.
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22
Remove from the oven and let the cookies cool for a few minutes on the baking sheet, then transfer to a rack to finish cooling.
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23
Put the remaining cookies on a second baking sheet and transfer it to the freezer.
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24
Freeze the cookies for at least an hour, until they are hard.
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25
Remove the baking sheet from the freezer and put the cookies in a freezer-safe heavy-duty resealable plastic bag, rolling out the excess air before you seal it.
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26
Return to the freezer and store for up to 3 months.
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27
Bake the frozen cookies for 15 to 20 minutes, until lightly golden.
