Put the coconut milk, brown sugar and salt in a large saucepan.
Whisk together ingredients over medium heat until the brown sugar dissolves.
Increase the heat and bring to a boil. Simmer until the mixture is reduced and begins to turn thicker and darker in color (this should take about 30 minutes). Stir the mixture occasionally.
Transfer the sauce to small jars to cool. When completely cold, cover it and refrigerate for up to 1 month.