Preheat the oven to 350 degrees.
Chop the nuts if needed and crush the biscotti into coarse pieces (about the size of the nuts).
On a lined baking sheet, spread the biscotti and nuts into a single layer.
Bake the biscotti and nuts for 6-8 minutes until the nuts are toasted. Remove and cool.
Using a double boiler, heat the chocolate chips and the butter over low heat until the chocolate melts and a smooth, silky mixture is achieved.
Remove from the heat and stir in the coffee until well incorporated.
Lightly fold in the toasted nuts and biscotti and the orange zest, careful not to crush the biscotti, but making sure everything is well coated.
Cover and refrigerate for 1 ½ to 2 hours or until the chocolate is moldable but not too firm.
Remove from the refrigerator and place half of the mixture onto an 18-inch-long piece of plastic wrap. Using your hands or a spatula, form the mixture into a log shape about the size of a sausage. Roll up the chocolate log in the plastic wrap and twist the ends. Once wrapped, roll on the counter to round the log if needed. Repeat with the second half.
Refrigerate both logs for at least 1 hour, until firm. They should feel firm enough to slice.
Place the powdered sugar in a plate. Remove the logs from the plastic wrap and roll in the powdered sugar until coated.
Slice with a serrated knife into ½ inch pieces and serve cold.