Bring a large pot of water to a boil. Salt generously, then add the spaghetti. Cook until al dente. Before draining, reserve a mug full (at least a cup) of the pasta water.

In a large skillet, heat 1 tablespoon of the olive oil over medium heat. Add the onion and cook until softened, about 5 minutes. Add the garlic and cook another 30 seconds, until fragrant. Add the tomato sauce and the Italian seasoning. Bring to a bubble, then reduce the heat to a simmer. Let the sauce cook and reduce for about 10 minutes.

Increase the heat slightly, and stir in the cream. Once the sauce is back to a simmer, add the cheese and stir until melted. Taste the sauce and season with salt and pepper, if needed.

In another skillet, heat the remaining 1 tablespoon of oil over medium heat. Add the shrimp and cook just until pink, 4-5 minutes.

Add the cooked pasta to the sauce, along with the shrimp. Stir to combine, adding the starchy pasta water as needed to loosen the sauce. Serve, topped with parsley if desired.