Hit the saute button on the Instant Pot and melt the butter.
Add the onion and cook until soft.
Whisk in flour and cook for 1 minute.
Whisk in one carton of chicken broth until smooth.
Add in the potatoes, carrots, celery, and remaining broth.
Set the manual cook time for 10 minutes. Do a quick pressure release.
Hit the saute button. Add in the peas, chicken, milk, poultry seasoning, salt and pepper, and cook until heated through. Do not boil - if it starts to boil, remove the pot from the Instant Pot.
Serve topped with pie crust croutons.