Preheat oven to 350 degrees

Cooke macaroni, drain. Transfer to 3-qt baking dish.

Melt butter in medium sauce pan over medium heat. Add flour, whisking until well blended, about 2 minutes. Gradually add milk, whisking vigorously and constantly. Bring to simmer. Reduce heat to low and add 2 1/2 cups American cheese and whisk until melted. Whisk in remaining ingredients.

Pour cheese sauce over macaroni and stir to coat. Sprinkle remaining 1/2 cup American cheese, paprika, and red pepper flakes over dish.

Bake until cheese is browned on top and bubbling around edges, about 40-45 minutes.