Fill a large pot with water, place over high heat and bring to a boil. Add a small handful salt to water and add pasta. Cook pasta, stirring occasionally, until soft with a small ‘bounce’, 8-9 minutes.
Drain pasta, reserving 1/3 cup pasta water, and set both aside.
Place a large skillet over medium heat. Once skillet is hot add oil and sauté onion and garlic for 2 to 3 minutes, or until aromatics begin to slightly caramelize. Season with salt and pepper.
Add tomato paste and stir together. Continue to stir until paste turns bright red, 2 to 3 minutes.
Deglaze skillet with vodka and stir together until vodka evaporates. Stir in crushed chili peppers and cook for 1 minute. Add reserved pasta water to skillet and stir together until smooth, about 1 minute. Season with salt and pepper.
Stir in crushed tomatoes. Simmer for 5 minutes.
Stir cream into sauce until mixture is smooth. Reduce heat to medium-low and simmer together, about 3 to 4 minutes. Stir in Parmesan and continue to simmer until sauce is smooth, glossy and has thickened enough to coat the back of a spoon, 2-to 3 minutes.
Stir in butter, in small pieces until fully melted and sauce is glossy.
Add cooked pasta to sauce and toss together until fully coated. Season with salt and pepper.
Serve with more grated Parmesan, basil leaves and crushed red pepper flakes, if using. Serve.