I looked an many variations of this sauce. Some were completely off base from what I was wanting. (Nutmeg in a TexMex sauce?) I cobbled this one together after reading through all those variations. Turned out to be just what I wanted.
1/4 cup butter
1/4 cup flour
1 1/2 cups chicken broth
1 1/2 cups sour cream
1 can or 1/2 cup cooked diced green chiles
1 teaspoon kosher salt
1 teaspoon black pepper
In a medium saucepan, melt the butter. Whisk in the flour and make a roux. Cook the roux until the flour smell is gone. About 5 minute, whisking continually.
Slowly whisk in the chicken broth. Bring to a boil, reduce the heat and whisk in the sour cream. Once the sour cream is incorporated add in the green chiles, black pepper and add the salt to taste. Simmer over low for 15 minutes.