In a large bowl, beat together butter and salt with a mixer at medium speed until smooth and creamy, 1 to 2 minutes, stopping to scrape down sides of bowl.
With mixer at low speed, gradually add confectioners’ sugar to butter mixture, alternately with buttermilk, beginning and ending with confectioners’ sugar and beating just until combined. Add vanilla extract, beating until incorporated. Increase speed to medium. Beat until frosting is light and fluffy, 1 to 2 minutes, stopping to scrape down sides of bowl as needed. Use immediately.
Recipe by TeaTime Magazine at https://teatimemagazine.com/banana-blueberry-oat-cakes-recipe/