Add olive oil to a large pan and heat it over medium heat.
Once the oil is hot, add onions and cook for 2-3 minutes, stirring frequently.
Add garlic and cook for another minute.
Now add tomato paste and cook for 2-3 minutes, stirring often.
Add vodka (if using) and cook for 1 minute. To make this dish without vodka simply omit this step.
Add heavy cream and pepper flakes and cook for 1 minute, stirring often until the sauce thickens.
Finally, add in your pasta, ½ cup of pasta water, and butter and stir until the butter is melted and the pasta is coated completely with the sauce.
Add some more pasta water if the sauce looks thick. Stir in parmesan cheese.
Taste for salt and pepper and add if needed. Garnish with fresh basil and serve immediately.