In a heavy-bottomed saucepan, warm the milk over medium heat, stirring occasionally until it reaches110*F.
Make the roux:
Meanwhile, in a separate heavy-bottomed saucepan, melt clarified butter over medium heat.
Stir the flour into the melted butter a little bit at a time, until it is fully incorporated. Cook until the flour taste is gone and the roux has a light blond color. Remove from heat.
Using a wire whisk, slowly add the roux to the warm milk, whisking vigorously to make sure it's free of lumps.
Attach the bay leaf to the onion using the cloves, and add them to the sauce.
Simmer for about 20 minutes or until the total volume has reduced by about 20 percent, stirring frequently to make sure the sauce doesn't scorch at the bottom of the pan. The resulting sauce should be smooth and velvety. If it's too thick, whisk in a bit more milk until it's just thick enough to coat the back of a spoon.
Remove the sauce from the heat. Retrieve the clove-stuck onion and discard. Carefully pour the sauce through a wire mesh strainer lined with a piece of cheesecloth.