Fill the Bonny Sweetened Condensed Milk into cleaned jam jars and close them securely. Depending on the size of the jars, you will need 1-3 glasses. The advantage of this method is that you can see the colour of the condensed milk through the jars.
Place an old kitchen towel inside a big pot to avoid clattering jars and put the jars into the pot.
Fill the pot with hot water, so that the jars are completely covered, and bring it to a boil.
Let it simmer for 2 hours until the condensed milk gets a caramel colour. Ensure that there is enough water to completely cover the jars at all times during cooking.
Carefully remove the jars from the boiling water and allow to cool down completely before opening.