1 Tb. butter
2 Tb. flour
1 (14 ½ oz.) can diced tomatoes
1-2 Tb. chopped mixed fresh herbs (optional), i.e. basil, rosemary, thyme or Italian seasoning
1 ½ cups shredded mild cheddar cheese
½ cup milk
2 Tb. grated Parmesan cheese
½ tsp. dry mustard
½ tsp. salt
4 cups cooked elbow macaroni (about ½ lb. dry macaroni)
Melt the butter in a large nonstick skillet over medium-high heat. Add the flour and cook, stirring constantly, until golden, about 1 minute. Add the tomatoes and cook, stirring constantly, until the mixture bubbles and thickens slightly, 2-3 minutes.
Stir the cheddar cheese, milk, Parmesan cheese, mustard, and salt into the skillet. Cook, stirring constantly, until the cheese melts and the mixture is smooth, 2-3 minutes Stir the pasta into the skillet and cook until heated through and well coated, 1-2 minutes. Let stand 2 minutes before serving.