This is one of the recipes from Country Living Magazine's March 2012 feature: The Casserole Makes a Comeback. We tried and it was an instant hit in our family. This would be a great use for leftover roasted chicken or turkey.
Preheat oven to 350 degrees Fahrenheit. Season chicken with salt and pepper, toss with 2 tablespoons oil, and bake in a cast-iron skillet until cooked through, about 30 minutes. Let cool, shred, and set aside.
Meanwhile, in a large pot over medium-low heat, melt butter. Add chiles; cook until soft, about 4 minutes. Add garlic; cook for 1 minute. Whisk in flour for 1 minute. Whisk in broth until thickened, about 6 minutes. Stir in sour cream, ¼ cup cilantro, cumin, and cayenne. Transfer to a blender, add tomatillos, and puree. Pour 1 cup mixture in each of 2 buttered 9-by-13-inch baking dishes.