1. Preheat oven to 375°F (190°C) and grease a baking dish.
2. In a skillet over medium heat, cook ground beef until browned. Drain excess grease and stir in taco seasoning and salsa. Simmer for 5 minutes.
3. Toss cooked pasta with sour cream and half of the cheddar and mozzarella cheeses. Season with salt and pepper.
4. Layer half of the pasta mixture into the baking dish. Spread the beef mixture on top, then layer the remaining pasta. Sprinkle the rest of the cheeses over the top.
5. Bake for 20-25 minutes, or until the cheese is melted and bubbly. Broil for an additional 2-3 minutes for a golden crust, if desired.
6. Serve warm with tortilla chips, guacamole, or sour cream on the side.