Preheat your oven to 180 degrees celsius (fan-forced) and lightly grease a 6 cup baking dish.
Place the cornflour and 100 grams of brown sugar into your Thermomix bowl and mix for 5 seconds, speed 6 to combine. Scrape down the sides of your Thermomix bowl and transfer the mixture to a small bowl and set aside until needed.
Without washing the bowl, place the butter into your Thermomix and cook for 2 minutes, 60 degrees or until melted.
Add the self raising flour, remaining brown sugar (50 grams), milk, vanilla extract and 2 tablespoons of golden syrup and egg to the Thermomix bowl and mix for 10 seconds, speed 4. Scrape down the base and sides of your bowl and mix for a further 5 seconds, speed 4 to combine. Transfer the mixture to your baking dish.
Combine the cornflour and remaining brown sugar in a small bowl, before sprinkling over the top of the pudding.
Carefully combine the boiling water with the remaining 2 tablespoons of golden syrup and pour over the top of the mixture before popping into your oven to bake for 35 minutes or until the pudding is cooked when tested with a skewer.