Mix the soy milk and sugar in a saucepan on low heat, stirring often until all the sugar melts; about 3 - 5 minutes
Bring milk and sugar to a simmer and simmer for 30 minutes. Be careful not to bring it to a high boil or it will spill over, making a mess. Do not stir the milk while it is simmering as it may crystalize.
After 30 minutes, it should be a greyish brown color. Pour it into a glass jar and leave to cool for at least 20 minutes.