Heat milk in a saucepan over medium heat until it begins to boil. Bring saucepan away from the heat and pour into a heatproof jar or small bowl.
Allow the milk to cool for about half an hour or until it feels comfortably warm to the touch. (there will be a shiny layer on the surface of the milk; just skim it off with a spoon.)
Spoon the natural yoghurt into the warm milk. Cover the jar or bowl and leave in a warm place to allow the culture to set. (do not stir or blend the mixture.) the process will take about seven to eight hours depending on the room temperature.
* Use any commercialised natural (not flavoured) yoghurt which you can find at most supermarkets and neighbourhood provision shops as the "starter" for your yoghurt culture.