Place the cinnamon stick and milk in a pan and bring to boil. Turn off the heat and leave to infuse for 5 minutes.
In a large whisk together the egg yolks and sugar, until thick and creamy.
Whisk in the ground cinnamon.
Discard the cinnamon stick and strain the hot milk over the egg yolk mixture and whisk continuously.
Pour the custard mixture back into the pan and cook on low heat for 10 minutes.
Stir the mixture constantly until it is thickened and coats the back of a wooden spoon.
Whisk the custard into the double cream, in a bowl sat over some ice.
Whisk until the mixture is fairly thick.
Cover the bowl with a clingfilm and chill for 2-4 hours or overnight (for better results, chill overnight).
Pour into an ice cream machine with the paddle running and churn the ice cream according to the machine instructions.
When serving the ice cream, take out of the freezer and leave to soften for a few minutes.