Boil the cheese tortellini according to package directions until al dente. Drain and set aside.
In a large skillet over medium heat, cook the ground beef or sausage with chopped onion until browned and crumbly. Drain excess fat. Add minced garlic and cook for 1 minute. Pour in marinara sauce, Italian seasoning, basil, salt, and pepper. Simmer for 5 minutes.
In a separate bowl, blend softened cream cheese and sour cream until smooth.
In a large mixing bowl, combine cooked tortellini, meat sauce, cream cheese mixture, 1 cup mozzarella, and ¼ cup Parmesan. Stir gently to coat evenly.
Grease a 9x13-inch baking dish. Spread the mixture evenly and top with remaining mozzarella and Parmesan.
Bake at 350°F (175°C) for 25–30 minutes until hot, bubbly, and golden brown on top.
Let the casserole rest for 5 minutes before serving. Garnish with fresh basil or parsley if desired.
