Bring a large pot of salted water to a boil and cook the penne until al dente, reserving 1/2 cup of pasta water before draining.
Heat olive oil in a large skillet over medium heat, then sauté onion until soft and translucent, about 4–5 minutes.
Add garlic and red pepper flakes, cooking for 30 seconds until fragrant but not browned.
Pour in the vodka and simmer for 2–3 minutes until slightly reduced and the alcohol smell cooks off.
Stir in crushed tomatoes and simmer for 8–10 minutes until the sauce thickens slightly and deepens in color.
Reduce heat to low and stir in heavy cream, salt, and black pepper, mixing until the sauce turns smooth and pink.
Add butter and Parmesan cheese, stirring until melted and glossy.
Toss the cooked pasta into the sauce, adding a splash of reserved pasta water if needed for a silky consistency.
Serve warm, topped with additional Parmesan and fresh basil if desired.