Heat butter in a heavy sauce pot over low heat. Add flour and make a white roux. Cool roux slightly.
In another saucepan, scald the milk. Gradually add it to the roux, beating constantly.
Bring sauce to a boil, stirring constantly. Reduce heat to a simmer.
Stick the bay leaf to the onion with the clove and add to the sauce. Simmer at least 15 minutes, or if possible, 30 minutes more. Stir occasionally while cooking.
Adjust consistency with more hot milk, if necessary.
Season very lightly with salt, nutmeg and white pepper. Spic flavor should be dominant.
Strain the sauce through china cap lined with cheesecloth or very fine sieve. Cover and spread with melted butter on the surface to prevent skin from forming.
Keep hot or cool in a water bath for later use. Can also store in Thermos.