1 Lightly oil a large baking tray. Put the sugar into a pan with 125ml (1/2 cup) of water. Stir over a medium heat until the sugar has dissolved. Increase the heat and boil for 8–10 minutes until a golden caramel forms. Stir in the nuts and pour onto the tray. Leave to set until hard.
2 Put 400g of the plain chocolate into a bowl. Put the instant coffee, cream and butter into a pan and heat until the butter has melted then bring to the boil. Pour onto the chocolate and stir until smooth. Chill for 30 minutes.
3 Put the hazelnut praline into a food processor and pulse until coarsely chopped. Stir into the chocolate mixture and return to the fridge and leave for about 2 hours until firm.
4 Roll the mixture into balls and then place on a tray lined with baking parchment. Chill for 1 hour.
5 Melt the remaining white and dark chocolate separately in bowls over pans of hot, but not boiling water. Once melted cool until of a coating consistency. Coat half the truffles in white chocolate and half in plain chocolate. Place on the lined tray and leave to set. Any surplus chocolate can be melted and drizzled over the set truffles.