Add the milk to a medium-size saucepot over low heat until it scalds. See notes.
Whisk in the roux until it is completely mixed in and smooth and bring just to a boil to thicken, and then turn the heat back down to low.
Next, make a 1” slit into the top of the onion and push the bay leaf into the slice and press the clove into the onion as well and then place the entire thing right into the bechamel sauce and cook for 15 minutes to infuse the flavor.
Add in the nutmeg, salt, and pepper and mix with a spoon.
Strain the sauce through a fine-mesh strainer like a chinois or some cheesecloth in a regular strainer. The sauce should be silky smooth.
Serve.
Notes
Make Ahead: You can make this sauce up to 2 days ahead of time.How To Store: Keep it covered in the refrigerator for up to 4 days. Do not freeze the sauce as it will break when thawing it.How to Reheat: Simply place your desired amount into a small saucepan and whisk over low heat until thick.You’ll know it’s scalded if you tilt the pan back to yourself and see bubbles clinging to the bottom of the pan but not sticking to it.If the sauce gets too thick when making it or reheating it, simply add a ¼ cup of hot milk at a time until it is to a thinner consistency.You must wait for the sauce to boil after mixing in the roux for it to thicken other wide, it will remain on the thinner side.