Béchamel sauce

Let the butter melt and foam well in a high pot.

Add all the flour at once and mix vigorously to ensure the flour and butter are well combined and homogeneous.

Let it cook for another 2 minutes so you don't get a floury taste.

Add half of the cold milk and whisk vigorously to eliminate lumps and stir until you have a smooth thick mass.

Now add the rest of the milk and whisk until you have a thick white sauce.

Season with pepper, salt, and grate some nutmeg in.

You can optionally add a few drops of lemon juice to freshen up the flavor of the sauce.