Bechamel sauce

Bechamel sauce:
Butter 100gr
Flour 100gr
Milk 1 litre
1 studded onion
Melt the butter in a thick-bottomed pan.
Add the flour and mix in.
Cook for a few min over a gentle heat without colour.
Remove from the heat to cool the roux.
Gradually add the warmed milk with the onion studded with clove and stir until smooth.
Allow to simmer for 30min.
Removes the onion, pass the sauce through a conical strainer.
Cover with a film of butter to prevent a skin forming.