Bring a large pot of salted water to a boil. Add the penne pasta and cook according to package instructions until al dente, about 8-10 minutes. Reserve 1/2 cup of pasta water, then drain the pasta and set aside.

While the pasta cooks, heat olive oil in a large skillet over medium heat. Add the diced onion and sauté for 3-4 minutes until softened and translucent.

Stir in the minced garlic and red pepper flakes. Cook for 1 minute until fragrant, being careful not to burn the garlic.

Add the tomato paste to the skillet. Cook for 2-3 minutes, stirring constantly, until the paste darkens slightly and caramelizes.

Pour in the vodka. Let it simmer for 1-2 minutes, scraping up any bits from the pan bottom, until most of the alcohol evaporates.

Reduce the heat to low and stir in the heavy cream. Simmer gently for 3-4 minutes until the sauce thickens slightly. Season with salt and black pepper to taste.

Add the drained pasta to the sauce, along with the reserved pasta water if needed to loosen the consistency. Toss everything together over low heat for 1-2 minutes.

Remove from heat and stir in the grated Parmesan cheese until melted and creamy. If using, add butter for extra silkiness.

Serve immediately, garnished with chopped fresh basil and additional Parmesan.