Using an electric mixer, beat the butter on high until light and fluffy, 3 to 5 minutes. Reduce mixer speed to low. Gradually add the sugar, then the vanilla and salt, and beat until smooth, scraping down the sides of the bowl as necessary.
Makes 4 1/2 cups
The frosting will keep in the refrigerator for up to 1 week. Bring to room temperature and, using an electric mixer, beat on low until light and fluffy before using.