Roughly crush the hazelnuts, then toast in a frying pan over a low heat until lightly golden. Leave to cool.
Tip the spread into a bowl and stir in a quarter of the evaporated milk until you have a smooth mixture. Stir in the remaining evaporated milk, then fold in 100 g (3½ oz) toasted hazelnuts.
Churn in an ice-cream machine according to the manufacturer's instructions. Transfer to a plastic freezerproof container and freeze.
Alternatively, freeze the mixture in a shallow container or tray for 2 hours until half-frozen, then tip into a bowl and whisk thoroughly to break up any ice crystals that may have formed. Return the mixture to the container and the freezer. Repeat the process at hourly intervals until the mixture is smooth and almost set. Finally, transfer the ice cream to a plastic freezerproof container and freeze until firm.
Remove the ice cream from the freezer 10 minutes before serving to soften slightly; it is best eaten within 48 hours. Scatter with the remaining hazelnuts and serve.