In the bowl of a stand mixer fitted with the whisk attachment, beat mascarpone, confectioners’ sugar, vanilla, and salt at medium speed until well combined, 1 to 2 minutes, stopping to scrape whisk and bottom and sides of bowl. With mixer on low speed, add cold cream in a slow, steady stream, beating until well combined; scrape whisk and bottom and sides of bowl. Beat at high speed until mixture is light and fluffy, 1 to 2 minutes. Cover and refrigerate for up to 3 days; stir before using.