With a handheld mixer or stand mixer fitted with a whisk attachment, beat butter on high speed for about 3 minutes or until creamy and lightened in color, scraping down the bowl as needed.
Add confectioners sugar, cocoa powder, 3 Tbsp heavy cream, 2 tsp vanilla extract, and 1/4 tsp salt.
Beat on low speed until sugar is incorporated then increase to medium/high speed and beat for 3 minutes, scraping down the bowl several times to ensure everything is well blended. Add another Tablespoon of heavy cream if needed to thin the frosting.