*Percent Daily Values are based on a 2,000 calorie diet. Your daily values may be higher or lower depending on your calorie needs.
**Nutrient information is not available for all ingredients. Amount is based on available nutrient data.
(-)Information is not currently available for this nutrient. If you are following a medically restrictive diet, please consult your doctor or registered dietitian before preparing this recipe for personal consumption.
Cook macaroni as directed on package, omitting salt.
Meanwhile, melt butter in large saucepan on low heat. Add onions; cook and stir 3 to 5 minutes or until crisp-tender. Whisk in flour and mustard; cook 2 minutes. Gradually whisk in milk until blended; cook on medium heat 3 to 5 minutes or until thickened, whisking constantly. Add 2 cups cheese; cook 1 minute or until melted, stirring constantly.
Drain macaroni. Add to sauce; stir to evenly coat. Stir in tomatoes. Pour into 8-inch square baking dish sprayed with cooking spray; top with remaining cheese.