3/4 stick (3 ounces) unsalted butter, chilled and cut into small pieces
1 cup granulated sugar
3 extra large eggs
2-1/2 cups unbleached all purpose or pastry flour, plus extra for dusting
1/2 teaspoon baking soda
1/2 teaspoon baking powder
1/8 teaspoon kosher salt
3/4 cup (3 ounces) raw, unsalted, shelled whole California pistachios
1/2 cup (3 ounces) California Zante currants or California raisins
Preheat the oven to 325°F; adjust the oven rack to the middle position.
Fill the bowl of the electric mixer with warm water and let stand for 2 to 3 minutes. Empty the warm water from the mixing bowl and wipe it dry with a kitchen towel. Using the paddle attachment, starting on low speed, cream the butter. As it starts to soften, increase the speed to medium. Cream the butter until smooth, about 1 to 2 minutes, scraping the sides of the bowl down as needed. Add the sugar, mixing until well blended, about 1 minute.
In a small mixing bowl, whisk together 2 of the eggs. Add them in 3 portions to the butter mixture, mixing on medium speed between each addition.
In a large mixing bowl, stir together the flour, baking soda, baking powder and salt, to combine thoroughly. Add half the flour mixture to the creamed butter and mix on medium-low speed for about 1 minute; then add the remaining half and mix until almost combined, about 1 more minute.
Add the pistachios and the currants and mix until thoroughly combined, about 1 minute longer.
Line a baking sheet with parchment paper. Lightly dust a smooth working surface and your hands with flour. Turn the dough out on the work surface and divide it into 2 equal pieces. Working with 1 piece of dough at a time, roll it out into a log, about 1 3/4 inches in diameter and 10 inches long. It is important to work the dough firmly to ensure that there are no air pockets in the middle of the log. Transfer the log to the lined baking sheet. Repeat with the remaining dough, placing the logs about 4 to 5 inches apart. Flatten each log slightly, to form a loaf about 3 inches wide and 11 inches long.
Separate the remaining egg, reserving the white and saving the yolk for other uses. Brush the top of the loaves lightly with the egg white.
Bake the loaves until they fall, expand in width to about 4 inches wide and are firm to the touch and lightly golden, about 35 minutes.
Remove the loaves from the oven and allow to cool completely, at least 6 hours.
Preheat the oven to 200°F. Line baking sheets with parchment paper. Using a very sharp serrated knife, slice the loaves thinly, on the bias to form individual cookies. Arrange the biscotti, closely spaced, on the baking sheets.
Bake the biscotti until firm and dry, about 20 to 30 minutes. Remove the biscotti from the oven and allow them to cool.
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