In a saucepan, add the cream and sugar, stir well to dissolve the sugar. Turn the heat to medium high heat and stir often until the cream begins to boil.
Turn the heat to low and simmer, giving an occasional stir, until there's a slight reduction in the liquid, about 6 minutes or so.
Pour the heated cream and sugar into a mixer bowl. Add the chocolate, butter, vanilla, and salt, stirring lightly until everything has melted. Set the mixer bowl in an ice bath to cool for a few minutes.
If you have a handheld electric mixer, use that while the mixer bowl is in the ice bath. If you are using a standing mixer, wrap ice packs or bags of ice around the bowl as best you can.
Beat the mix on medium until the frosting is fluffy, has thickened, and has a beautiful glossy shine. Frost the cake right away.