Cook tortellini according to package directions. Meanwhile, in a small bowl, combine the mayonnaise, milk, 1/4 cup Parmesan cheese, lemon juice and garlic; mix well. Drain tortellini and rinse in cold water; place in a large bowl. Add the romaine and remaining Parmesan. Just before servingg , drizzle with dressing and toss to coat. Top with croutons and enjoy.