Melt the butter in a saucepan over medium heat. Then add the sugar and stir occasionally until the sugar is no longer grainy and almost completely melted. Turn the heat down, stir in the cream and stir for about 3 minutes on low heat and then 7 minutes on medium heat. Then remove from the heat, let stand for about 3 minutes and then stir in the vanilla flavor and salt. Fill into the storage jar and let it cool down completely to room temperature first.