In the bowl of a stand mixer fitted with the paddle attachment, beat butter and salt at medium speed until smooth and creamy. With mixer on low speed, gradually add confectioners’ sugar, beating until combined and stopping to scrape bottom and sides of bowl. Beat in cream and vanilla. Increase mixer speed to high, and beat until pale and fluffy, 1 to 2 minutes. Add food coloring (if using) to brighten the frosting. (See Note.) Use immediately, or store in an airtight container at room temperature for up to 2 days or refrigerate for up to 1 week. If refrigerated, let come to room temperature and beat at medium-high speed with the paddle attachment to soften and smooth before using.