1Pour the milk and cream into a medium heavy-based saucepan. Stir over medium heat for 6-8 minutes until bubbles just start to form around the edge of the pan, do not boil. Remove from the heat.
2Put the egg yolks and sugar in a large heatproof bowl. Whisk until pale and creamy. Pour ½ cup (4 fl oz) of the hot milk mixture over the eggs and sugar and whisk to combine. Add the remaining milk mixture to the egg mixture, whisking to combine.
3Wash and dry the saucepan. Pour the mixture back into the pan. Stir constantly with a wooden spoon over low heat for 10-12 minutes, until the custard has thickened and coats the back of the wooden spoon, do not boil.
4Remove from the heat. Add the hazelnut spread and whisk gently until the custard is smooth.
5Strain the custard into a heatproof bowl and cover the surface directly with plastic wrap to prevent a skin from forming. Refrigerate for 4 hours until cold.
6Pour the chilled mixture into the ice cream bowl. Set the ice cream maker to the desired setting and churn.
7Add the hazelnuts once the machine specifies to add in Mix-Ins.
8Once the gelato is frozen transfer to a freezer-safe container, just large enough to contain the gelato. Freeze for 4 hours or overnight for firmer gelato.
9Scoop into bowls and serve with extra toasted hazelnuts.
10Store gelato in the freezer for up to 2 weeks. The gelato will become very firm after freezing overnight, so remove from the freezer and stand at room temperature for 5-10 minutes before serving for easier scooping.