In a clean bowl, cream together the butter and sugar until pale and fluffy, then gradually beat in the eggs one by one.
Sift the flour and fold it into the creamed mixture with the milk, salt and cinnamon.
Grease a 1-litre/1¾-pint pudding basin and spoon in the golden syrup.
Pour the batter mixture on top of the syrup and cover with buttered greaseproof and foil and tie with string. Place on a trivet in a large pot with water to steam. Steam for 1½ hours.
While this is steaming make the perry custard.
Heat the milk with the cream, perry and vanilla pod and bring slowly to the boil. Remove from the heat.
Beat the yolks in a separate clean bowl with the heated cream mixture and add the sugar until well blended. As the egg yolks warm, the cream will thicken to create custard. Keep stirring until the custard is thick enough to coat the back of a spoon.
Once the sponge pudding has steamed, turn it upside down on a plate and shake gently. Serve with the custard.