Preheat oven to 350. Line a heavy large baking sheet with parchment paper. Whisk the flour and baking powder in a medium bowl to blend. Using an electric mixer, beat the sugar, butter, lemon zest, and salt in a large bowl to blend. Beat in the eggs, one at a time. Add the flour mixture and beat just until blended. Stir in the pistachios and cranberries. Form the dough into a 13 inch long, 3 inch wide log on the prepared baking sheet. Bake until light golden, about 40 minutes. Cool for 30 minutes. Place the log on the cutting board. Using a sharp serrated knife, cut the log diagonally into ½- to ¾-inch thick slices. Arrange the biscotti, cut side down, on the baking sheet. Bake the biscotti until they are pale golden, about 15 minutes. Transfer the biscotti to a rack and cool completely. Keep stored in an airtight container for up to a week.