Add the milk and sugar into a small, heavy bottomed saucepan.
Heat it on a low heat until the sugar has dissolved.
Once all of the sugar has dissolved bring the mix to a simmer over medium low heat. Do not stir once the mix starts to simmer otherwise it can crack and crystalize.
Gently simmer for roughly 35-40 minutes, or until the milk has darkened to a creamy color, has reduced by half and thickened slightly. You may notice some foam forming on top, gently skim it off with a spoon.
When ready, remove from the heat and pour into a jar to cool. Let the condensed milk cool completely before putting on the airtight lid. Just note, it thickens up a lot after a few hours in the fridge.
Store in a labeled jar in the fridge and it will last for 6 months.
