Heat a large pot of lightly salted water to boiling. Carefully scoop out 1 cup and pour over sun-dried tomatoes in a small heatproof bowl. Let stand 5 minutes.
Meanwhile, cook rigatoni as per package directions, 14 minutes. Drain.
While pasta cooks, heat milk over medium heat until bubbly. Remove from heat and whisk in cream cheese, provolone and mozzarella until melted (mixture will be a little stringy). Stir in cornstarch-water mixture and return pan to heat. Bring to a simmer, stirring until smooth.
Drain and finely chop sun-dried tomatoes. Stir into pasta, along with sauce and basil. Top with a little freshly ground black pepper, a pinch of salt, and Parmesan, if desired.