Preheat the oven to 325°F (160°C). Grease a 9" x 13" casserole dish and set aside.

Bring a large pot of salted water to a boil. Cook the pasta until 1-2 minutes shy of al dente, then drain (do not rinse).

In a large stockpot over medium heat, melt the butter.

Sprinkle the flour into the melted butter and whisk constantly to form a smooth roux. Cook for 1-2 minutes to remove the raw flour taste.

Add salt, white pepper, paprika, and cayenne to the roux and whisk to combine. Taste and adjust seasoning as needed.

Slowly whisk in the whole milk and heavy cream, then increase heat to medium-high, whisking until the sauce thickens (about 3-5 minutes).

Reduce heat to low and whisk in 3 cups of the shredded cheese a handful at a time until fully melted and smooth. Adjust thickness with additional milk if necessary.

Pour the cheese sauce over the drained pasta and gently fold until the pasta is thoroughly coated.

Transfer the mixture into the prepared casserole dish and sprinkle the remaining 1 cup of cheese on top.

Bake for 25 minutes or until the top is golden and bubbling. For extra browning, use the broil setting for an additional 1-2 minutes, watching closely.

Let rest for 5 minutes before serving.