Put 2 tablespoons of the butter in the Instant Pot and press "Saute". Once the butter has melted, add the diced pancetta and saute for until the fat is rendered -- about 3 minutes.
Add the shallot or onion and saute until soft and translucent -- about 2 minutes. Add the garlic and saute for just 1 minute.
Add the vodka and deglaze the pot while scraping up any stuck on bits.
Add 1 1/2 cups of the marinara, plus the broth, tomatoes, and remaining 2 tablespoons of butter. Mix well. The butter need not melt fully.
Lay the pasta on top but do not stir. Simply spread it out with a spoon and then gently press most of it into the liquid.
Secure the lid, move the valve to the "sealing" position, and press the "keep warm" button. Then press the "High Pressure" button, and set the timer for 6 minutes. Quick release when done.
Stir in the remaining 2 cups of marinara, the oregano, heavy cream, Parmesan, and cream cheese, stirring until all has melded -- about 2 minutes. Serve with extra grated Parmesan cheese!