Boil a generously salted pot of water for the penne and cook it al dente according to package directions.
Meanwhile, add the oil and butter to a skillet over medium heat. Sauté the onion for about 5 minutes or until softened (ok if it lightly browns).
Stir in the garlic and cook for about 30 seconds.
Add the vodka and let the sauce bubble for 30 seconds or so.
Stir in the tomato paste until you've got a smooth mixture.
Stir in the cream, and reduce heat to medium-low. Let the sauce warm through. I find this sauce thickens up very quickly (within a couple minutes), but feel free to cook it a little longer to thicken it up even more.
Season with salt & pepper as needed. Toss with the drained pasta (if needed, thin the sauce out with chicken broth.)
Serve with freshly grated parmesan cheese, if desired.
