Prepare sausage based on preference; see notes below.
Bring a large pot of water seasoned with 1 tablespoon of olive oil to a boil over high heat. Add the pasta. Cook according to package directions EXCEPT undercook by 2 minutes. Drain the pasta in a colander and toss with a tablespoon of olive oil to keep it from sticking.
Sweat onion in a large skillet with 1 tablespoon of the olive oil and the unsalted butter over medium-low heat until softened and transparent, about 5 minutes.
Reduce the heat slightly, and slowly add 1 cup of chicken stock, the diced tomatoes with their juices, the oregano, basil, red pepper flakes if using, salt, and some freshly cracked pepper to the skillet with the onions and garlic. Stir well to combine.
Boil the remaining cup of chicken stock in a microwave-proof bowl or measure cup in the microwave. Remove carefully from the microwave, and add the tomato paste to the hot chicken stock and stir to dissolve. Add to the skillet and stir.
Turn the heat down to low. Cut the cream cheese into a few pieces and then add to the skillet with the tomato sauce. Stir the sauce until the cream cheese has fully melted in and the sauce is very creamy. Add the heavy cream and stir again.
Add the pasta and stir until it is well coated in the creamy tomato sauce. Taste and adjust the salt and pepper as needed.
Turn the heat to the lowest setting. Place a lid on the skillet and allow to simmer for 5 minutes. Stir. Replace the lid and again simmer for another 5 minutes. Sauce will be thicker and pasta will be considerably more tender.
Remove the skillet from the heat but leave the lid in place on the skillet. Allow the pasta to rest an additional 5 minutes.
Stir the pasta well. Ladle into individual pasta bowls and garnish with Parmesan cheese and fresh basil leaves. Alternatively, mount all of the pasta in a large serving bowl. Offer Parmesan cheese and fresh basil leaves with the pasta tableside.