Bring a pot of salted water to boil and cook pasta according to package directions. Reserve ½ cup pasta water and drain pasta. Set aside.
In a sauté pan over medium heat, whisk together heavy cream and pesto until smooth. Cook until lightly bubbling, then whisk in grated parmesan to melt.
Add the cooked pasta and, if desired, some of the reserved pasta water. Stir to coat the pasta with the sauce. Season to taste. If adding protein or vegetables, add now and stir until warmed through.
Serve pasta with additional parmesan cheese for topping.