I'm dairy free so I've substituted the butter and milk for plant based versions. 
Milk mixture:
I've added some fresh garlic and coriander  in the roux . As well as some cayenne pepper and salt once I've added the milk. 
I used my immersion blender to roughly blend everything before I poured the milk mixture in. 
Once the it was in the pot I put some celery salt in which completely elevated the taste.