Bring a large pot of salted water to a boil and cook the penne until al dente, according to package instructions. Drain.
In a skillet over medium heat, add 1 tablespoon of olive oil and fry the sausage until browned and crispy, breaking it up into smaller chunks. Remove from the skillet and set aside.
Place the skillet back over medium heat, and add the butter, garlic, and onions. Cook until the onions are soft and translucent. Add the crushed red pepper flakes and cook for another minute.
Carefully add the vodka (if your stove has an open flame, you can turn it off before adding it to prevent flare-ups), and bring to a simmer. Simmer for 3 minutes, stirring occasionally.
Add the tomato puree and bring to a simmer once again. Turn down the heat to low. When the mixture stops bubbling, add the heavy cream, black pepper, and salt to taste.
Stir in the cooked sausage (reserve some sausage for topping if you like), cooked pasta and parmesan cheese, and serve with plenty of additional parmesan for garnish.