Melt the sugar over medium-high heat until it becomes an amber-coloured liquid (it resembles liquid honey). I recommend using a medium pot, as the mixture will bubble and double in volume as it cooks.
When the sugar has melted, add the butter. It needs to be at room temperature and cut into chunks, as this will help it melt in the sugar more quickly. Stir constantly with a whisk.
Combine the vanilla extract and the cream, and pour the cream into the sugar mixture as soon as the butter has been incorporated. Having the cream at room temperature will decrease the risk for splattering caused by the difference in temperature.
After the cream, add the salt and continue boiling for one more minute. Set aside from the heat and give it a final stir. Transfer to a jar and let cool to room temperature before using.