Mix together the double cream, milk and orange zest in a medium saucepan and warm through. Set aside for 1 hour to infuse.

Mix the ricotta in with the cream mixture and heat in a medium saucepan until just under a boil.

In a large bowl whisk together the egg yolks and caster sugar until smooth.

Pour the ricotta mixture into the egg mixture in very slow and steady stream whisking constantly.

When everything is combined pour back into the saucepan and heat until just under a boil and the mixture has thickened.

Strain to remove the zest, then chill for at least 4 hours.

Decant into ice cream tubs and freeze for at least 8 hours before serving.