What you need:
5 tablespoons of butter (1/4 cup plus 1 tablespoon)
4 tablespoons of all purpose flour
4 cups of milk
1/2 teaspoon nutmeg
1/2 teaspoon salt 

What to do:
In a deep sauce pan melt the butter on medium heat. Add the flour, whisking to remove any clumps. Continue to cook on medium heat until the roux comes to a caramel colour, whisking continuously. 

In the meantime, in another saucepan heat your milk until almost boiling but remove from heat right before it comes to a boil. 

Once the roux is at the desired colour add the hot milk one ladle at a time whisking throughout to avoid clumping and burning. Bring the mixture to a boil and then turn down the heat and continue to cook for another 10-15 minutes. You'll notice that the béchamel sauce has thickened. The test for the proper consistency will be that it will coat a spoon when dipped into the sauce but will not stick like pudding. 

Remove from heat and add the salt and nutmeg. Put aside and let sit for 15 minutes to properly set. Enjoy with your favourite pasta, fish, chicken or anything else that needs a little something extra.