In a small saucepan, melt the butter over medium heat. Once the butter has melted, gently swirl the pot and continue to cook until the butter has browned. The butter is finished when it has turned dark amber and smells nutty.

Pour the browned butter into a medium heat-proof bowl or glass measuring cup. Cover, and refrigerate until solid.

Using a hand held mixer, beat the butter for a few seconds or until smooth.

Add the icing sugar, milk, vanilla, and salt. Beat on low until the icing sugar is fully incorporated. You might want to cover the bowl with a tea towel to prevent the icing sugar from flying about.

Once the icing sugar is blended into the butter, increase the speed to high and beat until the icing is very light and fluffy. Stop and scrape down the side of the bowl a few times. When it looks good, keep beating. Beat for at LEAST 5 minutes, and ideally for up to 10 minutes. The long beating produces a very smooth and creamy icing.