In a large pot of salted boiling water, cook the penne pasta according to package instructions until al dente. Reserve 1 cup of the pasta water, then drain the pasta and set aside.
In a large skillet over medium heat, add the olive oil. Once hot, add the diced onion and sauté for about 5 minutes until translucent. Stir in the minced garlic and red pepper flakes, cooking for an additional minute until fragrant.
Pour in the crushed tomatoes and bring the mixture to a gentle simmer. Allow it to cook for about 5-7 minutes, letting the flavors meld together. Season with salt and pepper to taste.
Reduce the heat to low and slowly stir in the heavy cream, mixing well until the sauce is smooth and creamy. Let it simmer for another 3-4 minutes, stirring occasionally.
Add the cooked penne to the sauce, along with some reserved pasta water a little at a time until you reach your desired sauce consistency. Mix well to coat the pasta evenly with the sauce.
Stir in the grated Parmesan cheese until melted and well incorporated. Taste and adjust seasoning with more salt, pepper, or red pepper flakes if desired.
Plate the pasta in bowls and garnish with fresh basil leaves and additional Parmesan cheese as desired.
Notes
Adjust the red pepper flakes to your desired spice level.