Bring 450ml (15fl oz/2 scant cups) water to a boil in a medium saucepan. Reduce the heat to a gentle simmer and add in the Assam tea bags, cardamom pods, star anise, cloves, vanilla extract and soft light brown sugar. Simmer for 2-3 minutes, or until the sugar has dissolved, then remove from the heat, cover and allow to cool and infuse.