Bring a large pot of salted water to a boil and cook penne according to package instructions until al dente. Drain and set aside.
In a large skillet, heat olive oil over medium heat. Sauté the chopped onion until softened, about 5 minutes.
Add the garlic and red pepper flakes and cook for 30 seconds until fragrant.
Pour in the vodka and simmer for 2–3 minutes, letting the alcohol cook off.
Stir in the crushed tomatoes and bring to a simmer. Let cook for 10 minutes, stirring occasionally.
Reduce heat to low and slowly stir in the heavy cream. Simmer for another 5 minutes.
Add the Parmesan cheese and stir until melted and creamy. Season with salt and pepper to taste.
Toss the cooked pasta with the sauce until well coated. Serve hot with fresh basil or parsley, if desired.