4 T. (1/2 stick) unsalted butter, melted and cooled, plus more for pan
2/3 c. shelled pistachios
1 c. (4 oz.) graham-cracker crumbs
1/4 c. sugar
1 T. grated lime zestPreheat oven to 350. Brush in 8-inch square baking dish with melted butter. Line bottom with parchment paper, leaving 2-inch overhang on two sides. In a food processor, finely grind pistachios with graham-cracker crumbs, sugar, and zest. Blend in butter. Press mixture into bottom and 1/2 inch up sides of prepared pan. Bake until lightly browned, 8 to 12 minutes. Cool crust, 30 minutes.
For the Filling:
2 large egg yolks
1 can (14 oz.) sweetened condensed milk
1/2 c. fresh lime juice
In a large bowl, whisk together egg yolks and condensed milk. Add lime juice; whisk until smooth. Pour filling into cooled crust; carefully spread to edges. Bake until set, about 15 minutes. Cool in pan on rack; then chill at least 1 hour before serving. Using parchment paper overhang, lift out of pan, and transfer to a cutting board. With a serrated knife, cut into 16 squares, wiping knife with a damp kitchen towel between each cut. To store in refrigerator, cover with plastic wrap.