1/2cupbutter1 cube, ideally 85% fat European style butter
1teaspoonreal vanilla extract
Place butter in a small saucepan over medium heat. When butter has melted, whisk in remaining ingredients until very shiny and smooth (sugar has dissolved completely). Remove from heat and allow to cool slightly.
Check consistency of icing: it should be thin enough to be pourable, but not so thin that it runs off the sides of the sugar cookie. If too thick, whisk in more water a few drops at a time. If too thin, whisk in more sugar until the icing reaches your desired consistency.
Transfer icing to small pitcher and swirl artfully over cooled sugar cookies. Let icing cool and harden. Serve.
If your powdered sugar is at all lumpy, be sure to sift / sieve it to remove any lumps before adding to the butter.
This recipe makes enough for icing about 25, 3-inch round sugar cookies.