Ube is a purple yam that is well-known for its use in Filipino desserts. The extract gives the condensed milk a vibrant purple color and a nutty, vanilla-like flavor.
Add the milk and sugar to a saucepan and cook on low heat for 30-40 minutes. Avoid stirring the mixture after the sugar has dissolved until the liquid has reduced by about half.
Remove from the heat and stir in the ube extract.
Allow the condensed milk to cool to room temperature before transferring it to a food-safe jar or container. Optional: Use a fine-mesh sieve to strain the sweetened condensed milk into your container for an extra smooth finish.