In a medium saucepan, combine brown sugar, water, and sweetened condensed milk over medium heat.

Bring the mixture to a gentle simmer, whisking continuously until all ingredients are fully combined.

Once the sugar is completely dissolved, remove from heat.

Stir in vanilla extract and salt, mixing well.

Let the syrup cool to room temperature, then transfer it to a clean, airtight container.

Store in the refrigerator for up to one week.