In the bowl of a stand mixer fitted with the paddle attachment, beat butter, lemon zest, and salt at medium speed until creamy, 1 to 2 minutes, stopping to scrape sides of bowl. With mixer on low speed, gradually add confectioners’ sugar alternately with buttermilk, beginning and ending with confectioners’ sugar, beating just until combined after each addition. Increase mixer speed to medium; beat until light and fluffy, about 2 minutes, stopping to scrape sides of bowl. Reduce mixer speed to low; beat for 1 minute to release some air bubbles. Use immediately.
Recipe by Bake from Scratch at https://staging.bakefromscratch.com/spiced-prune-cake-lemon-buttermilk-frosting/