Heat the oven to 350°F. Grease a 9×13-inch baking dish.
Boil the noodles in salted water to al dente (1–2 minutes shy of package directions). Drain very well.
12 ounces elbow macaroni
Toss the hot pasta with melted butter, then mix in 2 ½ cups cheddar, ½ cup Monterey Jack, and all of the Velveeta until it starts to melt and coat.
¼ cup unsalted butter, 4 ounces Velveeta
In a large bowl, whisk the eggs, evaporated milk, whole milk, sour cream, salt, pepper, paprika, dry mustard, garlic powder, and hot sauce.
2 large eggs, 12 ounces evaporated milk, ¾ cup whole milk, ½ cup sour cream, 1 teaspoon salt, ½ teaspoon paprika, ½ teaspoon ground mustard, ½ teaspoon garlic powder, ¼ teaspoon ground black pepper
Stir the custard into the cheesy pasta, and pour into the prepared dish. Top with the remaining ½ cup cheddar and ½ cup Monterey Jack.
Bake for 30–35 minutes or until the edges are set and bubbling and the center is creamy. Broil 1–2 minutes at the end if you want a deeper golden brown top.
Let the mac and cheese stand for 10 minutes so it sets but stays creamy, then serve.