Begin by bringing a large pot of salted water to a boil. Cook the pasta (penne or fettuccine) according to package instructions until al dente. Reserve 1 cup of pasta water, then drain the rest in a colander.
In a medium saucepan, heat the olive oil over medium heat. Add the diced onion and sauté until translucent, about 3-4 minutes.
Add the minced garlic to the pan and cook for an additional 30 seconds until fragrant.
Pour in the diced tomatoes (with juices) and bring the mixture to a simmer. Cook for about 5 minutes, allowing the flavors to meld.
Reduce the heat and stir in the heavy cream, dried basil, salt, and black pepper. Allow the sauce to simmer for another 3-4 minutes, stirring occasionally.
Add the cooked pasta to the sauce, tossing to combine. If the sauce is too thick, gradually add reserved pasta water until you achieve desired consistency.
Stir in the grated Parmesan cheese until melted and well blended into the sauce.
Serve immediately, garnished with fresh basil leaves if desired.