Sift and add the powdered sugar, vanilla extract, salt, and heavy cream and beat on low speed until the ingredients are just combined. Turn the speed to medium-high and beat for an additional minute, until the frosting is light and fluffy. Add more cream if you want a softer, creamier frosting. Place the frosting in a piping bag with an 8B open star decorating tip, and swirl the frosting on top of the cupcake.