Preheat the oven to 350°F. Grease a 9-x-13-inch baking dish and set aside.
Cook noodles, to al dente, according to the box instructions. Drain and set aside.
Meanwhile, in a large bowl, combine chicken, soup, sour cream, butter, chicken broth, garlic salt and pepper. Mix well, then stir in cooked noodles.
Pour into prepared baking dish. Sprinkle both cheeses on top and bake, uncovered, for 36–42 minutes, until cheeses are melted and bubbling.