Here's a white enchilada sauce I have made before with good results.
1/4 stick butter
2 TBS flour
1c chicken broth
1/2c sour cream
4 oz chopped green chilies
1/2 TBS of a southwest type of seasoning (I use Tasty Licks Acapulco Gold)
Pepper flakes to taste
Heat butter, stir in flour and make a blonde roux.
Stir in chicken broth and thicken.
Add everything else and heat through. DO NOT let come to a boil.
Some cilantro would make a nice garnish on top.