Boil macaroni. Preheat oven to 350°F. In small bowl, combine flour, salt, mustard, pepper, and cayenne. Melt butter in skillet over medium heat. Add scallions and saute about 2 minutes, until softened. Add flour mixture and cook for 3 minutes. Gradually whisk in milk. Cook 15 minutes, stirrings constantly until thickened. Remove from heat.
Stir in 1 1/2 cup cheese, and sour cream (if using). Add macaroni. Pour into greased 1 1/2 qt. baking dish. Top with remaining cheese and sprinkle with bread crumbs.
Bake 25-30 minutes, or until golden brown. Let sit 5 minutes before serving.
Calories From Fat
% Daily Value*
Total Fat 0g
Saturated Fat 0g
Trans Fat 0g
Dietary Fibers 0g
* Percent Daily Values are based on a 2,000 calorie diet.
* Nutrition information is estimated based on the ingredients and cooking instructions as described in each recipe and is intended to be used for informational purposes only. Please note that nutrition details may vary based on methods of preparation, origin and freshness of ingredients used.