Press the Saute button on the Instant Pot and add the butter. Once it has melted add in the onion, carrots, and celery and saute for 3-5 minutes. Add in the garlic and saute one minute.
Add in the potatoes and saute for 3 additional minutes.
Add in the chicken broth, pepper, and nutmeg. Lock the lid.
Press the Soup button and put the timer at 20 minutes. When the timer beeps quick release the pressure and then unlock the lid.
Add in the milk and instant potato flakes and stir well.
Ladle into bowls and serve with cheddar cheese and sour cream.
Notes
Recipe adapted from The "I Love my Instant Pot" Recipe Book by Michelle Fagone