Cut butter into equally sized small 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" and turn 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 melting butter is forming a white foam out of casein, a milk protein. The butter will get a golden color. Continue mixing it. 

Pro tip: If you have a cooking thermometer, you can follow the butter browning process. 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 on a beautiful chestnut-amber color (aka noisette color) with golden bits on the bottom of the pan and a hazelnut flavor.

Pro tip: The butter at 248°F (120°C) turns on a brown color and hazelnut flavor. If heated over 248°F (120°C), it risks burning and becomes unfit for consumption. So it is wise enough to use a cooking thermometer.

Immediately transfer the butter to a cold heatproof bowl to stop cooking from the 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.