Add butter to your Instant Pot and turn on sauté. Add the onions and cook about 4 minutes, until soft. Add the garlic and sauté for one additional minute. 

Add the chicken broth and potatoes. Place the lid on and ensure vent is set to “sealing”. Cook it on high pressure for 8 minutes. 

Once cooking is complete, do a quick release of the pressure. Remove lid and set the IP to sauté again. 

Whisk together milk and cornstarch. Add to the IP along with the heavy cream. Stir constantly and allow to simmer for about 5 minutes, until the soup has thickened up. 

Add salt & pepper to taste, then garnish with the cheddar cheese, bacon, and green onions before serving.