make the dough
Preheat the oven to 180°C / 355°C. In a large bowl beat together eggs, sugar, lemon zest, vanilla and 1/4 tsp of salt using an electric mixer. Beat for about 3 - 4 minutes. Add melted (cold) butter and milk (or Limoncello) while still beating. Incorporate baking powder, all-purpose flour, chopped walnuts, raisins, chopped hazelnuts, chopped almonds, and chopped pistachios. Knead into a dough using your hands.
divide the dough
Lightly sprinkle your working surface with flour. Place the dough on the floured surface and divide into two equal parts. Sprinkle each dough with flour and shape each half into a log that’s about 35 cm / 14 inches long. Place each log on a baking sheet lined with parchment paper. Sprinkle your hands with flour and flatten each roll to an even 1 cm or 1/2 inch thickness.
Place the baking sheet with the biscotti in the oven on the middle rack. Bake for 25 - 30 minutes at 180°C / 355°C. Take the biscotti out of the oven. Leave the logs on the baking sheet for about 5 minutes, then, while they are still warm, cut them diagonally on 2 cm or 1-inch cookies. Place the biscotti cookies back on the baking sheet lined with parchment paper. Place them in the oven and continue to bake for 3 minutes, then turn the cookies around and bake them for another 3 minutes on the other side of the cookie. Leave the biscotti to cool on a wire rack. Store in an airtight container for up to 30 days.