HEAT oven to 350°F.
COOK macaroni as directed on pkg., adding spinach for the last min. Cook bacon in large saucepan. Remove bacon; save drippings in pan.
ADD flour to drippings; cook and stir until bubbly. Gradually stir in milk. Bring to boil, stirring constantly; cook and stir 3 to 5 min. or until thickened.
STIR in 1 cup Cheddar and Parmesan; cook and stir until melted. Add bacon and macaroni mixture; mix well.
SPOON into 1-1/2-qt. casserole; top with remaining cheddar. Bake 20 min.