In a small pot combine cream, butter, vanilla and salt. Bring just to a boil and set aside.
Heat a heavy bottomed pot with high sides over medium high heat. Begin by sprinkling the granulated sugar over the bottom in a thin layer, when that begins to melt, sprinkle some more. Keep sprinkling until all the sugar is in the pot. As parts begin to melt, gently stir with a wooden spoon and break up any clumps that form. Continue to stir to distribute the sugar into any hot spots and use the already melted sugar to melt the rest. Once the sugar has melted stop stirring and swirl until a dark amber color is achieved.
If you have a hard time telling the color of the caramel, tilt the pot towards you so that there is only a thin layer. I find it easier to see that way. A medium amber is a perfectly acceptable color but I like to take mine to dark amber which is right when it starts to smoke but before it smells burnt.
Remove from the heat and place on a trivet. Slowly pour in your cream/butter mixture while constantly whisking. You don’t want to add the cream too fast or it will bubble up aggressively and could burn you. Don’t fear, just keep whisking. Once all the liquid is incorporated, pour into a heat safe bowl (glass, ceramic, pyrex, metal are all fine). Allow to cool to room temperature then pour into the storage container of your choice.