Beurre noisette, or brown butter, is butter gently cooked until the milk solids caramelise and it turns amber with a rich, nutty, roasted hazelnut aroma. It takes about 10 minutes and is perfect for sweet and savoury dishes.
Cut the butter into small, equal pieces. Place butter in a light-colored heavy-bottomed saucepan or frying pan.
Melt butter over low or medium heat, stirring occasionally with a wooden spoon or silicone spatula. At first, the butter will melt and get opaque; continue stirring.
Then the butter will start to sputter or "sing," turning yellow. You will hear a crackling noise which will gradually decrease. This stage means the water evaporates, indicating that the water content is evaporating and the fat is popping. Decrease the heat if necessary.
The next stage of butter melting is the formation of a white foam from casein, a milk protein. The butter will turn golden. Continue mixing it. Pro tip: If you have a cooking thermometer, you can monitor the butter's browning. The melting point of butter is 104°F (40°C), it boils at 158°F (70°C), and water evaporates at 212°F (100°C).
Finally, the butter will turn a beautiful chestnut-amber color (aka noisette color) with golden bits on the bottom of the pan and a hazelnut flavor. Pro tip: Butter at 248°F (120°C) turns brown and develops a hazelnut flavor. If heated over 248°F (120°C), it risks burning and becomes unfit for consumption (use a cooking thermometer).
Immediately transfer the butter to a cold, heatproof bowl to prevent further cooking from residual heat. You can also add a small piece of cold butter to stop the cooking.
To remove the brown bits of the liquid butter, let it sit for 3 minutes so the suspended particles settle to the bottom. Then pass it through a fine-mesh sieve or Chinois strainer into the bowl.
Leave it to cool to room temperature. Use it in a liquid state, or reserve it in the refrigerator and use it in a solid state.
Notes
Opt for a light-colored heavy-bottomed saucepan. The light-colored pan makes it easy to see the color changes, while the heavy bottom ensures even heat distribution.
Ensure the butter is cut into pieces for even cooking.
Always heat over medium-low heat and watch the cooking closely.
Continue stirring continuously to observe the color of the mixture under the bubbles.
Keep an eye on the butter and trust your senses: watch for color changes, the appearance of browned milk solids, and the smell of roasted hazelnuts.
Be careful with butter spits and splashes. Do not touch the contents of the pan. Wear a long-sleeve shirt.
Take the pan off the heat once the golden brown color is reached. You must stop cooking; otherwise, it will continue to brown and thus burn. Carbonization will result in burnt butter or black butter (beurre noir). You cannot use it for baking.
Remember that the best way to brown butter without burning is to use a cooking thermometer.