In a saucepan, melt the butter over medium heat. Once melted, add the flour and whisk until smooth to create a roux.

Cook the roux for a minute or two, stirring constantly. This step helps eliminate the raw flour taste.

Gradually add the milk to the saucepan, whisking continuously to prevent any lumps from forming.

Continue whisking the sauce until it thickens and reaches a smooth consistency. This process usually takes around 5-7 minutes.

Season the sauce with salt and optional spices, such as a pinch of nutmeg or a dash of pepper, according to your taste preferences.

Stir constantly during the cooking process to avoid scorching the bottom of the pan.