In a bowl, beat together butter, sugar and grated zest until light and fluffy.
Add the eggs, one at a time, beating well after each addition.
Sift in flour, baking powder and cinnamon.
Mix together naartjie juice, milk and 1 tablespoon golden syrup and add to egg mixture. Stir well to combine.
Butter a pudding bowl (or a heatproof bowl large enough to hold the batter). Add 2 tablespoons golden syrup into the base of the bowl.
Spoon in batter and cover bowl with a round of baking paper and tinfoil wider than the pudding bowl by about 4cm all round. Tie a piece of string tightly around the lip of the bowl to secure cover, and place on an inverted saucer in a large pot.
Fill the pot halfway with boiling water, cover with lid and simmer for 1½ hours, topping up the water if necessary.
Remove pudding and invert onto a serving plate. Serve with extra golden syrup, naartjie zest and custard or cream.