1 C brown sugar
4 Tbsp (1/2 stick) butter
1/2 C heavy cream or half-and-half (cream will make it thicker)
1 Tbsp vanilla
1 pinch salt
Mix all ingredients in a medium saucepan, over medium-low to medium heat.
Cook for 5 to 7 minutes while whisking gently, until thicker.
Serve warm, or refrigerate until ready to serve.