To brown butter.
Preheat a small sauce pan to Medium/Medium Low heat and throw your stick of butter in. It will start to bubble up a little as it melts down; swirl the pan around instead of stirring with a spoon. After about 5 minutes, the bubbles will begin to turn to a thick foam. Watch it carefully! The foam will turn from a nice white/cream to a tan color after a couple more minutes. Once that happens, and it begins to smell nutty and delicious, remove your pan from the heat.