Meanwhile, in 5-quart Dutch oven or saucepan, melt butter over low heat. With whisk, stir in flour and salt until smooth. Increase heat to medium; cook until mixture is smooth and bubbly, stirring constantly. Gradually stir in milk. Heat to boiling, stirring constantly. Boil and stir 1 minute. Remove from heat; gradually stir in cheese and chiles until cheese is melted. Stir in cooked pasta. Pour mixture into baking dish; sprinkle with crushed chips.