Melt the butter and decant it in order to recover casein and whey. Once clarified, it becomes resistant to high cooking temperatures (180 °C / 356 °F) without any risk of becoming brown or black.
Unsalted Gourmet Butter
Unsalted Tartine et Cuisine
Cut the butter into small pieces and place them in a saucepan.
Melt the butter over a low flame, without stirring
You can also melt it in a bain-marie, or in the microwave.
As the butter melts, the casein (the protein in the milk) forms a white scum on the surface. This should be removed.
Allow the melted butter to stand so that the whey sinks to the bottom.
Pour off the clarified butter, making sure you leave the whey in the bottom of the saucepan.
Clarified butter can be kept like normal butter.