First, melt butter over medium-high heat, then add the flour and coat all the flour in butter.
"Cook-Out" the flour. Allow the flour to absorb the butter. This will help ensure the Bechamel sauce will not be grainy.
Next, add in ⅓ of the Milk and stir constantly. The sauce will try to thicken. Add the remaining Milk at this point. Keep stirring. Allow the Milk to come to a soft boil. (Soft boil means the bubbles are breaking the surface, but not a full boil)
Once at a soft boil turn off heat. The sauce will thicken. If the sauce gets too thick for your purposes add a little more Milk to thin out the sauce. Remember the heat activates the Roux and thickens.
Add the Nutmeg, to taste. Stir and incorporate
Add the Onion with the Cloves to the pot.
Cover the pot for 4 to 5 minutes to allow the flavors to develop.