Bring cream, whole milk, corn syrup, sugar, cocoa powder and salt to a boil in a large saucepan. Whisk in a little more than half the chopped chocolate and vinegar. Reduce heat low-medium and cook for about 12-15 minutes or until the sauce starts to thicken and has the elasticity of hot fudge. At this point, remove pan from heat and whisk in remaining chocolate, butter and vanilla. Allow to cool before filling cupcakes.