PREHEAT oven to 350°F. Melt butter in large saucepan on low heat. Add flour and salt; mix well. Cook 2 minutes or until bubbly. Gradually add milk, stirring until well blended. Cook on medium heat until mixture boils and thickens, stirring constantly. Reduce heat to low; simmer 3 to 5 minutes or until thickened. Add 1-1/2 cups of the cheese; cook until melted, stirring constantly. Add macaroni; mix lightly.
SPOON into 1-1/2-quart casserole; sprinkle with remaining 1/2 cup cheese.
BAKE 20 minutes or until heated through.
