Step 1

In a tall heavy bottom saucepan, melt the butter on low-medium heat.  Add the brown sugar, corn syrup, rum, vanilla extract, a pinch of salt, and heavy cream.  Stir until melted.

Step 2

Cook at low to medium heat, stirring occasionally with a wooden spoon until the sugar dissolves and the sauce simmers and thickens.  Continue to stir occasionally throughout the process.  If the sauce simmers too high up in the pan, remover the saucepan from the heat and continue to stir.  Return the sauce back to the heat as soon as the sauce settles down.  Continue cooking for about 20 minutes.  The sauce should be thick enough to lightly coat the back of a wooden spoon.

Step 3

Turn off the heat and allow the sauce to come to room temperature. The sauce will continue to thicken as it cools.