Line a 23x12cm (9x5in) dish or tin with clingfilm and set aside. Put the chocolate in a large heatproof bowl.
Heat the cream in a pan until gently bubbling, then pour half over the chocolate, leave for 1 minute to melt a little, then mix with an electric whisk. Add the remaining cream and continue mixing until until smooth and glossy. (Adding the cream in two parts prevents the mixture splitting; if it does separate, whisk in a splash of cold cream to bring it back together.) Stir in the wine, and vanilla.
Pour the truffle mixture into the prepared tin. Smooth the top, then chill for at least 4 hours or overnight, to set.
Using a hot knife (dip in hot water then dry with kitchen towel), cut the truffles into bite-size squares. Keep chilled until ready to eat. If you like, dust with a little cocoa powder before wrapping, to stop them from sticking.
To alter the flavour, swap the Champagne for orange liqueur or brandy, if you prefer. You can also scoop the chilled mixture into rounds, using a teaspoon, for a more classic shape.
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