Heat a large pot or dutch oven on medium heat. Add olive oil, diced onions, and a pinch of salt. Stir frequently and cook until onions are soft and translucent, about 10 minutes. Add garlic and sausage. Break up sausage with your spoon and cook until sausage begins to brown and is no longer pink, about 5-10 minutes. Use a spoon to remove sausage and onion mixture from the pot and set aside on a plate. Drain excess grease.
In the same pot, add heavy whipping cream. Bring to a low steady boil. Cook for about 15 minutes, or until the cream is reduced in half and you can briefly see the bottom of the pot when you run your spoon along the bottom.
Add in the tomato sauce then the vodka to the cream. Stir until fully incorporated. Add onion and sausage mixture back to the pot and stir. Bring to a low boil then reduce heat to low to simmer. Cover and simmer for 15 minutes.
While the sauce is simmering, make the pasta. Bring a large pot of water to a boil and cook penne pasta until al dente (typically a minute or two before the suggested time on the box). Drain.
Add the pasta, peas, and parmesan to the sauce. Give it all a good stir for a minute or two. Serve hot with more freshly grated parmesan and chopped parsley (optional).
Notes
I often substitute the sausage for diced pancetta. Cook the pancetta until crispy.
To make vegetarian, omit the sausage. When you add the garlic to the pot you will only need to cook it for a few seconds.
You can make the sauce a few hours ahead by keeping covered on very low heat. Wait to add the pasta, peas, and parmesan until you are ready to serve.
I love the color that the peas give and it is a great way to sneak in veggies. If you don't like peas, leave them out.