In a heavy 3-quart saucepan, melt the sugar and water over medium-high heat. Whisk constantly until the sugar is dissolved.
Once the sugar mixture reaches a low boil, stop whisking and allow the mixture to continue boiling until it reaches a medium-dark amber color. This step can take a while, but be sure to watch the mixture carefully: if you step away, this is where it could burn. Every once in a while, swirl the pan to ensure even boiling.
As soon as the sugar mixture reaches that dark amber color, take it off the heat and immediately add the butter. Whisk briskly until the butter melts completely.
Slowly and carefully pour in the heavy cream and whisk to combine. The mixture may bubble as you whisk, which is normal.
Keep whisking the mixture until it is a gorgeous, luscious caramel sauce.
Pour the caramel sauce into glass jars to cool, uncovered.