Beurre noisette
brown butter
Beurre noisette is butter heated until the milk proteins caramelise. The name comes from the French for hazelnut and describes both the colour and the aroma of the finished fat.
It is made over medium heat in a light-bottomed pan so the colour stays visible. The butter passes through stages: it melts, then foams as the water evaporates, the foam subsides, and brown specks appear at the base. Those are the caramelising proteins, and they carry the nutty aroma.
Readiness is judged by smell and by the colour of the sediment. The gap between noisette and burnt butter is a matter of seconds, so pour it immediately into a cold container: in a hot pan the process continues.
The sediment is usually kept — all the flavour is in it — though it can be strained out if needed.
In pastry, noisette is indispensable in financiers and madeleines, where it supplies their characteristic nuttiness, and it also goes into shortcrust, sponges and ganaches.