For the bechamel sauce, boil the milk (or stock) with the onions, bay leaf, peppercorns and juniper berries for a bit.Meanwhile, melt the butter, stir the flour into the hot butter and let it foam once.
Pour in the strained milk (or cooking stock), stirring briskly with a whisk. Cook until the desired consistency is reached.
Stir constantly, as the sauce will set up quickly! Season the béchamel sauce to taste.