Cook pasta according to package directions; drain.

Meanwhile, brown ground beef and sweat the onion together in a large skillet over medium-high heat. When the beef is completely cooked through, drain off excess fat, return to skillet, and add garlic. Cook and stir 30 seconds. Add taco seasoning and salsa and stir to combine; reduce heat to low.

In a medium saucepan over medium-high heat, add cream cheese, milk, and sour cream and stir to combine. Cook until cream cheese is melted and mixture is thick and bubbling. Stir in shredded cheese.

Add cheese sauce and ground beef mixture to pasta and stir to combine. Top each serving with salsa and sour cream, if desired.