Pulse together half of the pistachios with half of the caster sugar until you have a very fine mixture. Roughly chop the remaining pistachios and reserve to one side.
Whisk together the egg yolks with the rest of the caster sugar until pale and thick. Combine the cream and pistachio and sugar mixture in a medium saucepan and bring to the boil. Pour over the egg yolk and sugar mixture whisking simultaneously until you have a smooth mixture.
Transfer back into the pan and cook on a low heat, stirring continuously with a wooden spoon until it thickens; usually 6-8 minutes. Remove from the heat and place in a large bowl of iced water in order to cool the custard quickly. Transfer to a clean bowl, cover and chill for 2 hours.
Remove from the fridge and stir the chopped pistachios into the custard base and churn the mixture until soft and thickened. Serve two scoops per bowl.
*This pudding is very rich and indulgent, so shouldn't be eaten too often. But it's perfect for those special occasions!
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