Melt 1/2 cup butter in a medium-size saucepan over medium heat.
Stir in 1 cup granulated sugar, 1 cup coconut milk, and 1 teaspoon vanilla extract. Bring to a boil over medium-high heat, stirring occasionally, and simmer for 4 minutes.
Allow to cool slightly and thicken before serving. Store in a heat-safe airtight container in the refrigerator.