In a medium sauce pan, over medium heat, melt butter. Once melted, add flour and whisk constantly to cook the flour and remove the flour taste. You'll know it's done when it smells nutty rather than like flour (you've just made a roux!). When flour is cooked, slowly add the HOT chicken broth/stock, whisking constantly to incorporate. Increase heat to medium-high and bring mixture to a boil. The mix will slowly begin to thicken. Once it boils, add in sour cream, cream cheese, green chiles, hot sauce, salt and pepper, whisking constantly. Bring back to a boil, give it another whisk to ensure all ingredients are incorporated and the cheeses have melted, then remove from heat. Serve immediately.
Notes
To prevent lumps, it's important that your broth/stock is HOT. If you add it cold to the roux, it'll seize up and create lumps.