Clarified butter is what you get when you heat butter to the point that the milk proteins curdle and settle out, the minerals and sugars clump and rise to the top, and much of the water boils away. What you’re left with is nearly pure butterfat.
What’s the advantage of that? Well, once all that’s done butter starts to behave a lot more like oil, and that’s a handy thing when you want the flavor of butter but also want to be able to subject it to high heat. If for instance you want to sauté with it or even fry in it. For the clarifying process has the effect of raising the smoke point of butter from around 325 degrees Fahrenheit to around 425 degrees Fahrenheit, which is pretty darn amazing.
Odds are you’ve clarified butter yourself at one point or another, even if you weren’t intending to do it. Maybe you melted several sticks to make a filo pastry of some sort. As you worked you noticed the foam on the top of the butter and the film on the bottom of the pan. Later when you returned to wash up, you noticed that the butter had remained a semi-liquid once it had cooled. Even when refrigerated it never returned to its former firm state.
What you had there was ghee. If you remember from some of the earlier posts, butter is an emulsion: tiny droplets of water inside a matrix of butterfat crystals, free liquid butterfat and some protein-encased butterfat blobs that managed to survive the butter making process intact. Heat wrecks that emulsion, and more that that it curdles those protein coats, breaking the butterfat globules and freeing the butterfat inside. The result is a mass of nothing but free fat which can never go back to the emulsion from whence it came.
Is clarified butter useful in baking? It certainly can be, especially in cake batters (génoise, madeleines) where you want the moist texture that oil provides without completely sacrificing the flavor you get from butter. I say “completely” because much of the flavor of butter comes from the sugars and minerals you lose in the clarifying process. And if it this moment you happen to be asking yourself: does this mean I shouldn’t clarify expensive butter? The answer is an unequivocal “yes.”