Preparation

• Preheat the oven to 350°F. Spray a 9X13 inch baking dish with nonstick cooking spray; set aside.
• Cook the pasta per package instruction, just to al dente, using 1 tablespoon of salt in the water. Drain. Dry the pasta pot and set aside.
• Melt the butter in a large, high-sided skillet. Sprinkle flour over melted butter and whisk for at least 1 minute to remove flour taste.
• Remove the skillet from heat and gradually add the milk and half-and-half, whisking constantly until smooth. Return to low heat and continue to whisk until sauce thickens about 4-6 minutes.
• Remove the skillet from heat and stir in American cheese, cheddar cheese, white cheddar, and Parmesan cheese. Stir in salt, black pepper, and dry mustard, and continue to stir until melted.
• Return drained pasta to the dried pasta pot then pour cheese sauce over it. Stir to combine well. Pour mixture into prepared baking dish.
• Sprinkle with finely grated cheddar cheese and bake, uncovered, until cheese is melted and the sauce is bubbly about 15 minutes.
• Garnish with green onion and serve.