Butter a 1.2 litre pudding basin and prepare circles of parchment and foil.
Pour 50g of golden syrup into the bottom of the basin.
Whisk 50g syrup, butter, sugar, and zest until light and fluffy.
Gradually whisk in the eggs and flour until the mixture reaches a dropping consistency.
Spoon the batter into the basin and smooth the top.
Pleat the parchment and foil to allow for expansion during cooking.
Secure the covers with string and create a handle for easy lifting.
Place basin on a trivet in a pan with water reaching halfway up the sides.
Steam over low heat for 1¾ hours, ensuring the water does not boil dry.
Rest for 5 minutes before inverting onto a plate and serving with extra syrup and custard.