Finely grate the zest of four of the oranges but juice the 6. Place the juice in the fridge for later. Heat the cream and the orange zest in a heavy based pan over a low heat. Bring up to scalding point then remove from the heat and leave to cool and infuse.
Place the egg yolks and sugar in a large bowl and whisk until thick and creamy. Pour in the infused cream and stir well. Rinse out the saucepan, return the mixture to it and place over a medium-low heat. Cook, stirring continuously, until you have an orange custard. Do not allow the custard to boil as it will curdle.
Place the custard in a clean bowl, when it has chilled stir in the juice from your oranges and a dash of Grand Marnier, cover and chill in the fridge overnight. This greatly improves both the flavour and texture of the finished ice cream.
The following day, churn in two batches in a 1.5L ice cream machine. Place churned ice cream in a tightly lidded container and store in the freezer until ready to use. Allow ice cream to soften in the fridge for an hour or so before eating. Use with a week.