In a large skillet over medium-high heat, sauté the onion until softened, then add the garlic and cook for an additional minute. Break up the beef into small pieces using a wooden spoon or spatula as it cooks. If you prefer a leaner option, there will be less excess fat to drain, but note that it may slightly affect the flavor compared to using 80% beef.
Add the taco seasoning to the skillet and stir well.
Pour in the beef broth, crushed tomatoes, and milk. Add the uncooked macaroni, cover the skillet, and allow it to come to a simmer. Reduce the heat and cook for approximately 15 minutes, or until the pasta reaches an al dente texture, stirring occasionally to prevent sticking and ensure even cooking. Initially, it may seem like there is excess liquid, but this is normal.
The pasta will absorb the liquid as it rests, resulting in a thickened sauce. It's best to consume this dish immediately if you've cooked the pasta directly in the sauce, as reheating may cause it to become dry. If reheating, you'll need to add extra liquid such as broth, water, or milk, but note that the flavor may be less intense and different from the original.
Reduce the heat and stir in 1 cup of shredded cheddar cheese and grated mozzarella cheese, combining them thoroughly. Remove from heat and serve. Optionally, you can also sprinkle ¼ cup of cheddar or mozzarella cheese on top of the pasta, cover the skillet, and allow the cheese to melt.
Serve the dish hot, accompanied by lime wedges on the side.