Add the olive oil to a large pot or dutch oven over medium heat.
Once the oil is hot, add the onion, sauté 3-4 minutes, then add the garlic and sauté for an additional minute.
Add the Italian sausage and cook through, 7-9 minutes.
Add the pasta shells, chicken broth, tomato sauce and Italian seasoning.
Stir to combine and bring to a simmer.
Cover, reduce heat to low and cook 15-20 minutes, or until pasta is tender.
Remove the lid, add the cream cheese, parmesan cheese and mozzarella cheese.
Stir until the cheese is melted, cooking for an additional 3-4 minutes.
Notes
Store any leftovers in an airtight container in the refrigerator for up to 5 days. Reheat a single portion in the microwave for 2-3 minutes. Or reheat more than one portion in a pot on the stove for 5-7 minutes, or until heated through.