Combine orange zest, butter, vanilla and sugar in a large bowl with an electric mixer until fluffy and light. Mix in egg white and eggs, one at a time. Sift together the flour, salt and baking powder, and gradually blend into the butter mixture until smooth, using a wooden spoon. Stir in the pistachio nuts, white chocolate and cranberries. Cover, and chill for 30 minutes or until the dough is no longer sticky. Preheat oven to 325F (165C). Line a baking sheet with parchment paper. Transfer dough onto a lightly floured surface and divide it in half. Roll each half into a flattened log about 12 inches long and 3 inches wide. Place on baking sheet, ensuring that each log is at least 3 inches apart. Bake for 30 minutes or until pale golden. Allow to cool enough to transfer to a cutting board. Cut logs crosswise and diagonally, making 1 inch thick slices. Return slices to baking sheet, and bake for an additional 15 minutes or until golden. Allow biscotti to cool completely on wire racks. Makes about 24.