Preheat the oven to 350F. Line a large cookie sheet with parchment paper.
In a medium bowl, whisk together the flour, baking powder and salt.
2 cups all purpose flour, 1½ teaspoons baking powder, ¼ teaspoon fine sea salt
In the bowl of a stand mixer, combine the sugar and lemon zest. Rub the zest into the sugar with your fingers until the sugar is damp and very fragrant.
⅔ cup granulated sugar, 1 tablespoon lemon zest
Beat in the butter, until lightened and fluffy, about 2-3 minutes.
Beat in the eggs, one at a time.
2 large eggs
Beat in the vanilla.
1 teaspoon pure vanilla extract
Beat in the flour mixture until just combined.
Stir in 1 cup of the pistachios.
1 cup + 2 tablespoons pistachios, chopped
Form the dough into a 13" long, 3" wide and 1" tall log on the prepared cookie sheet.
Bake the biscotti until light golden brown, about 40 minutes.
Cool the biscotti to room temperature, about 30 minutes.
Place the cooled biscotti on the cutting board. Using a sharp serrated knife, cut the log on a diagonal into ½" to ¾" thick slices.
Place the biscotti back on to the parchment paper. Bake for 15 minutes.
Once the biscotti are cooled, melt the white chocolate in a microwave safe bowl for 30 second increments, stirring after each increment, until melted and smooth.
1 ½ cup white chocolate, chopped
Dip the biscotti into the melted chocolate. Gently shake off any excess chocolate and place on a cooling rack to set. Sprinkle the chocolate with remaining chopped pistachios.