In a small pan:
6 tablespoons butter
1 1/4 cup [155 grams] powdered sugar
In the small pan, cook the butter over medium heat until little brown specks start to appear. Whisk the butter constantly and don't walk away because butter burns really, really, quickly. Don't ask me how I know.
As soon as the butter is browned transfer immediately to the bowl with the powdered sugar and salt. Whisk thoroughly. After a minute, it will come together and smoothen out. Let it cool for five or ten minutes and then dunk away! With the donuts, not your fingers.