Beurre noisette is made when the milk solids within butter caramelize, creating a nut-like aroma and taste.
Put cubes of unsalted butter in a saucepan over a medium heat. Let the butter melt, stirring frequently. (1)
Once the butter has melted it will begin to foam a little then subside, continue to cook stirring frequently (2) until the milk solids start to turn a light brown. (3)
Remove from the heat and pour into a tray, then leave to cool. (4)