French for hazelnut butter, it is butter cooked in the manner of Beurre Noir, until it turns the golden brown color of hazelnuts. It is a popular way to sauté and sauce meat, poultry, fish, and fruit; and also serves as a sauce for pasta and vegetables.
Beurre Noisette ('hazelnut butter', sometimes loosely translated as 'brown butter') is frequently used in French pastry production. Unsalted butter is melted over low heat and allowed to separate into butterfat and milk solids. The milk solids naturally sink to the bottom of the pan and, if left over gentle heat, will begin to brown.