Beurre noisette — brown butter — is made by cooking butter past the point of melting until the milk solids turn deep golden and the aroma becomes distinctly nutty. In a conventional hollandaise, clarified butter is used to remove water and milk solids entirely, producing a clean richness. Using beurre noisette instead retains those toasted solids (strained out just before use), adding a layer of nutty, caramelised depth that enriches the sauce without obscuring delicate flavours. Use a light-coloured pan so you can monitor the colour change accurately. Pour the browned butter through a fine sieve into a clean bowl the moment it reaches deep gold — it continues to darken in the pan after you remove it from the heat. Allow it to cool to approximately 60°C / 140°F before adding it to egg yolks; butter that is too hot will scramble them.