Add Ziti, heavy whipping cream, water, salt, pepper, onion and Italian seasoning.
Place lid on the IP.
Pressure cook on high for 3 minutes and natural release for 5 minutes. Follow the manufactures instructions for quick release.
Remove the lid; add cornstarch mixture and lemon juice.
Add ½ cup of grated Parmesan cheese at a time; stir and mix.
Press the cancel button.
Wait for 3 minutes before serving (cornstarch mixture will thicken the sauce). Watch the video for reference.