Cream together the butter and sugar in a clean bowl until pale and fluffy.
Gradually beat in the eggs one at a time.
Fold in the sifted flour, milk, salt, and cinnamon into the creamed mixture.
Grease a 1-litre pudding basin and add the golden syrup to the bottom.
Pour the batter over the syrup and cover with buttered greaseproof paper and foil.
Secure with string and place on a trivet in a large pot with water.
Steam the pudding for 90 minutes.
Heat the milk, cream, perry, and vanilla pod in a pan and bring slowly to a boil.
Remove from heat and whisk the hot liquid into a bowl containing the egg yolks and sugar.
Stir the mixture continuously until it thickens enough to coat the back of a spoon.
Turn the steamed sponge upside down onto a plate and serve with the custard.