In the bowl of an electric mixer fitted with the flat beater, beat the cream cheese, butter and salt on medium-low speed until smooth and creamy, 2 to 3 minutes. Reduced the speed to low, gradually add the confectioners' sugar and beat until incorporated. Add the vanilla and beat just until incorporated. Do not overmix or the frosting will incorporate too much air; it should be creamy and dense, like ice cream. Add milk, 1 tsp at a time, if frosting does not have a spreadable consistency.