Clarified butter is rendered butter once all the milk solids have been removed. When butter is melted, it separates into three layers. The top layer is a white frothy foam (the whey), to be skimmed and discarded. The bottom layer is the milk solids.
What’s left is a pure, golden liquid – clarified butter. If you keep simmering until all moisture has evaporated and the solids have begun to brown, your clarified butter will have graduated to ghee, with only the fat left. Strain through a fine sieve. Ghee keeps longer, takes on a nutty flavour and can be used to fry at higher temperatures than normal clarified butter.