Boil salted water and cook pasta until al dente
Reserve 1 cup pasta water
Heat olive oil and butter in a pan over medium heat
Add chopped onion and cook until soft
Add minced garlic and cook briefly
Stir in tomato paste and cook until darkened
Add vodka and simmer until reduced
Add heavy cream and stir until smooth
Season with salt, black pepper, and red pepper flakes
Add grated Parmesan and mix until melted
Add cooked pasta to the sauce
Toss with reserved pasta water as needed
Finish with more Parmesan and chopped basil or parsley