Preheat the oven to 350 degrees 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 36β42 minutes, until cheeses are melted and bubbling.
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Notes
Make ahead of time. We frequently make this tetrazzini recipe ahead of time. Just make it as instructed except don't top with the cheese or bake. Instead, cover tightly with foil or saran wrap and place in fridge for up to 24 hours before adding the cheese and baking.STORE leftovers in an air-tight container in the fridge for up to 3 days.FREEZE. Just make as instructed, cover tightly and freeze for up to 2 months. Just let thaw in the fridge overnight, add the cheese and bake in the oven.