RE: Easy Cauliflower Gratin and preparation of the Traditional Béchamel sauce.

The butter is melted. I add the flour all at once and mix the two together briskly without waiting too long. As soon as this is done, I start adding the milk little by little, never stopping to stir. Don't forget the corners of my pan :)

Can one add the flour little by little instead of doing it all at once ??