On medium heat, bring the mixture to a boil. Stir regularly, until it begins to simmer. Once it begins to simmer, reduce the heat to very low. Let the condensed milk simmer for around 45 minutes.
Remove from the heat and allow it to cool down completely. Once cool, transfer to a glass jar or container and refrigerate.
* Monk fruit sweetener, erythritol, allulose, or sugar free brown sugar.TO STORE: Leftover condensed milk should always be stored in the refrigerator, to avoid any spoilage. It will keep well, covered, for up to 4 weeks. Before using it, let it sit at room temperature for 30 minutes, for it to loosen up. TO FREEZE: Place the condensed milk in a sealable container, and store in the freezer for up to 6 months.