In a large bowl or stand mixer fitted with a paddle attachment, cream 1 cup unsalted butter and ½ teaspoon salt on low speed until pale and creamy.
1 cup unsalted butter
Add in 4 cups powdered sugar and 2 ounces heavy cream a little at a time, alternating between each, while mixing on low over the course of about 3 minutes. Add an additional ½ cup of powdered sugar or an additional 1 tablespoon of heavy cream at a time until desired consistency is reached.
4 cups powdered sugar, 2 ounces heavy cream
Add 1 tablespoon vanilla extract and increase the speed to high for about 2 to 3 minutes, and whip until the frosting is light and fluffy. Scrape down the sides every minute or so.
1 tablespoon vanilla extract, ½ teaspoon salt
Use as desired or store in an airtight container.