Love love love this sauce, it's perfect for dipping apples slices, putting over ice cream or as an addition to other desserts. It's super easy to make, the only tricky part is knowing exactly when to remove it from the heat. The best tip I can give is to remove it as soon as you see noticeable color in the syrup. It will darken considerably when the cream is added.
In a medium sauce pan, add water, corn syrup and sugar. Stir constantly over medium heat til mixture starts to boil. Then leave completely alone until the syrup just starts to turn amber. (Approx. 15 -20 minutes).
Remove from heat. SLOWLY add in the milk, stirring while doing so. It will bubble up and steam at this point so be very, very careful not to burn yourself.
Add softened butter, vanilla and salt, stir well then allow to cool before serving/storing.