Preheat the oven to 165°C (325F). Line a large baking sheet with parchment paper.
In a medium-sized bowl, sift and mix flour, baking powder, and salt and set aside.
Place sugar in large bowl of a stand mixer fitted with with paddle attachment. Add eggs, one by one, and mix on medium speed after each addition. Add lemon zest and mix to combine.
Add dry ingredients, mixing until just combined. Fold in pistachios using a spatula. Do not overmix.
Cover and chill the dough for at least 30 minutes (up to overnight)
Scoop half the dough mixture onto one side of the baking sheet lined with parchment paper. Form the dough in the shape of a log. If dough is too sticky, sprinkle with some flour until manageable. Repeat with the remaining mixture to form an equal-sized log on the other side of the baking sheet.
Bake in a preheated oven for 35 minutes (until lightly golden). Bring out of the oven and allow to cool for around 10-15 minutes.
Place baked logs onto a cutting board. Slice the logs in a sawing motion using a sharp/serrated knife (straight or diagonally) into ½-¾ inch thick biscotti.
Transfer sliced biscotti, sliced side up, back onto the baking sheet. Bake for another 15-25 minutes until dried and centers are slightly golden brown. Transfer to cooling rack to cool completely. Biscotti will harden as they cool.