Especially useful for preparing a roux:

For clarified butter, slowly melt unsalted butter over low heat. Don’t let the butter come to a boil, and don’t stir it. This allows the milk solids to separate from the liquid butter.

Once the butter has separated into three layers--foamy milk solids on top, clarified butter in the middle, and milk solids on the bottom--turn off the heat. Skim the foamy white solids from the top. Then ladle off the clarified butter. Be careful not to disturb the milk solids at the bottom of the pan.

Clarified butter can be used immediately. Or, let it solidify and keep it in the refrigerator for up to three to four weeks. Just re-melt to use. One pound of unsalted butter yields 1-1/4 cups clarified butter.

clarified butter is also known as ghee, though the preparation is a little bit different under that writeup. Happy Cooking! - thanks to nine9