Boil a large pot of salted water and cook the elbow macaroni until al dente. Drain and set aside.
In a large skillet over medium heat, brown the ground beef until fully cooked.
Drain excess fat from the beef and return to skillet.
Add the diced onion to the beef and sauté until softened.
Stir in the taco seasoning and cook for an additional 2 minutes.
Pour in the milk and bring to a gentle simmer.
Add the cooked macaroni to the skillet and stir until well combined.
Mix in 1.5 cups of shredded cheddar cheese until melted and creamy.
Taste and adjust seasoning with salt and pepper as needed.
Serve hot, topped with diced tomatoes, jalapeños, and remaining cheese.