Place the softened butter and powdered sugar in a stand mixer fitted with a whisk attachment. Beat the butter and sugar together until combined. The mixture will be thick.
Add the milk, salt, and vanilla extract and turn the mixer on high. Beat for 3 minutes. Scrape down the sides of the bowl using a rubber spatula. Beat for 2 more minutes until frosting is thick and fluffy.
Transfer to a piping bag to frost your favorite cake, cupcakes, or cookies!