Preheat the Oven: Preheat your oven to 350°F (175°C). Lightly grease a 9×13-inch baking dish with nonstick spray.

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

Prepare the Beef Mixture: In a skillet over medium heat, brown the ground beef until fully cooked. Drain any excess fat. Stir in the taco seasoning and Rotel tomatoes, then let it simmer for 5 minutes. Remove from heat.

Make the Cheese Sauce: In a large saucepan, melt the butter over medium heat. Whisk in the flour and cook for 1 minute, stirring constantly to avoid lumps. Gradually add the milk, whisking continuously until the mixture thickens (about 3–4 minutes). Stir in Velveeta cheese, black pepper, paprika, nutmeg, and salt. Continue stirring until smooth and fully melted.

Assemble the Dish: In a large mixing bowl, combine the cooked pasta, cheese sauce, and taco beef mixture. Stir until evenly coated.

Bake: Transfer the mixture to the prepared baking dish and sprinkle the remaining shredded cheddar cheese over the top. Bake uncovered for 10 minutes.

Broil for a Golden Top: For a crispy, bubbly cheese layer, broil for an additional 2 minutes before serving.