In a medium saucepan, over medium high heat, bring milk to a simmer. Add onion, clove and bay leaf, then remove from heat. Cover and set aside. After 20 minutes, remove the onion, clove and bay leaf.
In a heavy saucepan, melt butter over low heat. Add flour and whisk continuously for 2 minutes. Add 1/4 cup of the milk at a time, whisking to blend, until all is incorporated and sauce is smooth.
Over medium heat, Bring bechamel sauce to a boil for 30 seconds, whisking in salt, pepper and nutmeg. Stir constantly.
Croque Monsiuer
Preheat oven to 425 degrees Fahrenheit, with a cast iron, or preferred oven safe pan inside.
Butter 3 slices of the sourdough bread, turn over and layer on 2 slices of ham, 1 tablespoon of bechamel sauce, then 1 slice of gruyere on each.
Top each with remaining sourdough bread, one tablespoon of bechamel sauce, and another slice of gruyere.
Place each sandwich in warmed pan, baking until cheese is melted and slightly browed.
Serve sandwiches with a sprinkling of fresh chives, and dusting of nutmeg.
Use bechamel sauce immediately, or if preparing ahead of time, cover the surface with plastic wrap until ready to serve. Can be stored in the refrigerator for up to 2 days.