In a large bowl, stir together biscuits, hazelnuts, and pistachios.

In the top of a double boiler, combine chocolates. Cook over simmering water, stirring occasionally, until melted and smooth. Remove from heat. Whisk in chocolate hazelnut spread, milk, melted butter, orange zest and juice, confectioners’ sugar, vanilla bean paste, and salt. Add chocolate mixture to biscuit mixture, stirring until well combined.

Spoon half of biscuit mixture onto a sheet of plastic wrap, and shape into a compact, rough 9×2-inch log. Wrap in plastic wrap, smoothing, reshaping, and rewrapping log as needed to minimize air pockets or divots in surface; while holding ends of plastic wrap, roll log over work surface, creating a more rounded shape. Repeat with remaining half of biscuit mixture. Refrigerate until firm, at least 3 hours.

Unwrap logs; dust on all sides with confectioners’ sugar, shaking off excess. Using a serrated knife, cut logs into ¼-inch-thick slices. (See Note.)