Beat 400g sugar and eggs with an electric mixer in a large bowl until light and fluffy. Stir in the flour, baking powder, bicarbonate of soda, salt, vinegar and apricot jam. Pour in 475ml milk and stir until well combined. Spoon the batter into a greased, 2 litre oven-proof baking dish.
Bake in the preheated oven for 60 to 70 minutes or until a knife inserted into the centre comes out clean. Pierce the baked pudding several times with a skewer or fork.
Place 200g sugar, water, 250ml milk, butter and vanilla in a saucepan and stir over medium heat. When the mixture comes to a boil remove it from the heat and slowly pour the mixture over the hot pudding. Serve warm.