Get a thick and large sized baking sheet. Get parchment paper and line the baking sheet with it. Whisk flour and baking powder in medium sized bowl to blend together. In a large bowl combine the sugar, butter, lemon zest and salt with an electric mixer to blend all together well. After that add the eggs in 1 at a time and beat them. Then add the flour mixture and beat them until well mixed. Then stir in the pistachios and cranberries to the mix.
Roll the dough so that it makes a 13-inch-long, 3-inch-wide log and put it onto the prepared baking sheet. Bake it until it is light gold, or about 40 minutes. Then remove it from the oven and allow it to cool for 30 minutes.
Put the log onto the cutting board, then cut it diagonally into ½ to 3/4-inch-thick slices with a serrated knife. Afterwards put the biscotti cut side down onto the baking sheet and bake until pale golden, or about 15 minutes depending. Then move the biscotti to a rack so that they can completely cool down.
Stir the chocolate in a bowl put into a saucepan full of simmering water until the chocolate melts. After melted dip half of the biscotti into the melted chocolate, making sure to have no excess chocolate on. After they are all dipped, put the biscotti onto the baking sheet so that the chocolate can set. At this time sprinkle on the sugar crystals and refrigerate until the chocolate is firm, or about 35 minutes.
This dish doesn’t have to be made the same day as the meal. It can be prepared ahead of time and stored in some kind of airtight container for up to 4 days before. Or you can wrap them in foil and freeze them in resealable plastic bags up to 3 weeks.