Begin by whisking the heavy whipping cream, sour cream, instant coffee, and vanilla together until combined. Then, in a medium saucepan, melt the butter over medium heat. When the butter is melted, whisk in the sugar, cocoa, and salt until combined. It will be grainy, but that's okay. When the cocoa mixture is combined, slowly add in the wet ingredients and lower heat to "low". Allow the mixture to cook for 2-3 minutes on low heat, it should begin to thicken slightly. Don't allow to boil!