• Grease a 3-quart or 9×13-inch casserole dish with butter and set aside.

Cook the Pasta

• Bring a large pot of water to a boil over high heat. Generously salt the water with 1 tablespoon of kosher salt. Add the pasta and stir to prevent sticking. Cook according to package directions until al dente.
• Reserve ½ cup of the pasta cooking water. Drain the pasta well, toss it with 1 tablespoon of oil, and spread it in a single layer on a half baking sheet to cool quickly. Set aside.

Prepare the Cheese

• In a large bowl, toss all the cheeses together until evenly mixed. Divide the mixture evenly into two portions (1.25 pounds each): one for the sauce and one for layering later.
• Preheat the oven to 350°F.

Make the Cheese Sauce

• In a large dutch oven or pot, melt the butter over medium-low heat. If needed, increase to medium. When the butter begins to foam, whisk in the flour. Cook, whisking constantly, for 1 minute until the roux turns lightly golden.
• Slowly pour in the evaporated milk while whisking in a thin, steady stream. Continue whisking until the mixture is smooth.
• Add the heavy cream the same way—pouring slowly while whisking continuously to maintain a creamy texture.
• Whisk in the paprika, mustard powder, garlic powder, onion powder, ¼ teaspoon salt, and black pepper. Continue whisking constantly as the sauce comes to a gentle simmer over medium-low heat, then keep whisking for 3–5 minutes, until it thickens to the consistency of light gravy.
• Reduce the heat to low. Gradually add the first portion of cheese (1.25 pounds), whisking in small handfuls and allowing each addition to melt completely before adding the next.
• The sauce should be smooth and velvety—it should drape, not sit heavy. If the sauce becomes too thick, stir in 1–2 tablespoons of reserved pasta water (keep in mind it’s salted) or heavy cream until it loosens to the desired consistency.
• Turn off the heat. Add the cooked pasta and stir gently until every piece is fully coated. Taste and adjust seasoning with salt and pepper as needed.

Assemble the Casserole

• Spoon half of the mac and cheese into the prepared casserole dish and spread evenly. Sprinkle half of the remaining cheese mixture on top.
• Add the rest of the mac and cheese, then finish with the final layer of cheese.

Bake and Serve

• Bake uncovered for 15–20 minutes, or until the cheese is melted, the casserole is heated through, and the edges are lightly bubbling.
 For a golden-brown top, broil on high for 2–3 minutes, watching closely to avoid over-browning.
• Remove from the oven and let it rest for 5 minutes before serving. Garnish with chopped parsley, and serve.