Cook the pasta: Boil the penne in well-salted water according to the package directions until al dente. Reserve 1 cup of the pasta water, then drain.

Soften the onion: Heat the olive oil and butter in a large deep skillet over medium heat. Add the onion and cook for 4-5 minutes, until soft and translucent. Stir in the garlic and red pepper flakes and cook for 30 seconds until fragrant.

Caramelize the tomato paste: Add the tomato paste and cook, stirring constantly, for 2-3 minutes, until it darkens to a deep brick red and smells sweet and roasted.

Add the vodka: Pour in the vodka and stir, scraping up anything stuck to the pan. Simmer for 2-3 minutes to cook off the alcohol; the sharp smell will mellow as it goes.

Stir in the cream: Reduce the heat to low and stir in the heavy cream and salt until the sauce turns an even blush pink. Simmer gently for 2 minutes.

Melt in the parmesan: Stir in the parmesan until smooth. If the sauce looks tight, loosen it with a splash of the reserved pasta water.

Toss and serve: Add the drained penne and toss until every piece is coated, adding more pasta water a splash at a time as needed. Serve topped with fresh basil and extra parmesan.