For the bechamel, melt your butter on low heat in a medium-sized pot.  Once melted, add your flour, stir till a ball or more lumpy consistency appears.  Add your nutritional yeast and stir more.  Now, slowly add your milk and whisk aggressively while cooking on medium-high heat (the whole proces should take around 20 minutes).  Stir till you've added all your milk and a more silky smooth sauce comes together.  Add the nutmeg and stir even more!  At the last minute season to taste, remove from heat and set aside.