In a large, heavy saucepan, combine the sugar and water. Set over medium heat, stirring until the sugar dissolves. Increase the heat to high and cook, swirling the pan for even color, until the mixture turns a very deep amber.
Take the pan from the heat and carefully add the cream, butter and corn syrup: the caramel will sputter and steam.
Put the pan back on the stove and bring the mixture to a boil, whisking frequently to mix the ingredients. Continue boiling for a total of 3 minutes.
Let cool slightly, pour into jars, cover, and chill.
Notes
This sauce will keep in the refrigerator for 3 weeks, but it can be frozen for up to 3 months.