Put the chocolate in a medium heatproof bowl and heat in the microwave in 30-second intervals, stirring in between, until completely melted and smooth, about 3 minutes. In another medium bowl, cream together the granulated sugar and butter with an electric hand mixer until smooth, about 3 minutes. Beat in the melted chocolate, coffee and cocoa powder until thoroughly combined, scraping the bowl as needed. Stir in the biscotti, pistachios and walnuts.
Pour the chocolate mixture onto a large piece of plastic wrap and shape into a log about 2 inches in diameter and 12 inches long. Roll until the log is completely covered in plastic and refrigerate until firm, about 1 hour.
When ready to serve, remove the chocolate salami from the plastic wrap and dust with the confectioners' sugar. Wrap with butcher's twine for an authentic salami look.
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