Cook pasta in boiling water according to package instructions, then drain and set aside. save about a cup of pasta water for adding in later if needed.
heat a pan with olive oil on medium heat, add in onions and let cook until tender and translucent. add in vegan butter, milk, sour cream, cream cheese and Boursin garlic and herbs. Lower heat if needed, stir well and until sauce is smooth.
mix in seasonings to sauce and stir well. Add in pasta gradually and stir until sauce completely covers the pasta. gradually add in pasta water to make sauce slighter thinner (optional). add in mozzarella and stir well, let simmer for 3-5 minutes.