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1
Heat the oven to 350 degrees F and arrange a rack in the middle.
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2
Line a baking sheet with parchment paper; set aside.
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3
Whisk the measured flour, baking powder, and salt in a medium bowl to break up any lumps and aerate; set aside.
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4
Place the sugar and butter in the bowl of a stand mixer fitted with a paddle attachment and beat on medium speed until fluffy and light in color, about 3 minutes.
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5
Stop the mixer and scrape down the beater and the sides of the bowl with a rubber spatula.
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6
Add the eggs, zest, and vanilla and mix until combined, about 1 minute.
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7
Stop the mixer and scrape down the beater and the sides of the bowl with the rubber spatula.
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8
Turn the mixer to low and slowly add the reserved flour mixture, mixing until just combined.
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9
Add the cranberries and pistachios and mix until evenly combined.
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10
Turn the dough out onto a lightly floured work surface and divide it into 2 equal portions.
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11
Using your hands and flouring them as needed, shape each portion into a 10-by-1-1/2-inch rectangle.
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12
Transfer the rectangles onto the prepared baking sheet.
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13
Bake until light golden brown, about 30 minutes.
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14
Remove the pan to a wire rack and let cool for 15 minutes.
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15
Meanwhile, reduce the oven temperature to 300 degrees F.
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16
Remove the rectangles to a cutting board (reserve the baking sheet and parchment).
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17
Using a serrated knife, cut each rectangle crosswise on a slight diagonal into 1/2-inch-thick pieces that are about 4 inches long.
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18
Discard the end pieces.
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19
Place the remaining pieces flat on the reserved baking sheet, spacing them at least 1/4 inch apart.
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20
Bake for 15 minutes.
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21
Flip the biscotti and bake until the tops are dry to the touch and light golden brown, about 15 minutes more.
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22
Place the baking sheet on the wire rack and let the biscotti cool completely on the sheet, at least 30 minutes.
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23
Melt the chocolate, if using, in a small saucepan over low heat.
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24
(Alternatively, melt the chocolate in the microwave, stirring every 30 seconds to avoid burning.)
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25
Transfer it to a small resealable plastic bag, cut about 1/16 inch off one bottom corner, and drizzle the chocolate over the biscotti in a zigzag pattern.
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26
Let the biscotti sit until the chocolate has set, about 30 minutes.
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27
The cookies can be stored in an airtight container at room temperature for up to 1 week.
