Preheat the oven to 350°F and lightly grease a 9×13-inch baking dish with nonstick spray.

Bring a pot of salted water to a boil and cook the elbow pasta for 1–2 minutes less than the package directions. Drain thoroughly and set aside.

Brown the hamburger meat in a skillet over medium heat until fully cooked, draining off any excess fat. Stir in the taco seasoning and undrained Rotel, then let the mixture simmer for 5 minutes before removing it from the heat.

In a separate large saucepan, melt the butter over medium heat. Whisk in the flour and cook for 1 minute, continuing to whisk constantly to prevent lumps.

Gradually add the milk, whisking until the mixture becomes smooth and starts to thicken, about 3–4 minutes.

Stir in Velveeta cheese along with nutmeg, paprika, salt, and black pepper. Continue stirring until the cheese has fully melted and the sauce is velvety.

In a large mixing bowl, combine the cooked pasta with the cheese sauce and taco meat mixture. Stir until all components are evenly coated.

Transfer the mixture into the prepared baking dish and sprinkle the shredded cheddar cheese over the top.

Bake uncovered for 10 minutes. For a golden, bubbling top, broil for an additional 2 minutes before serving.