Push saute & combine the sliced leeks, cabbage, kale, and butter and saute for 7-8 minutes or until wilted. Turn the saute function off.
Add the potatoes and broth, and place the cover on the Instant Pot. Seal the valve, and push manual (high) for 7 minutes.
When it's done, release naturally for 10 min and then do a quick release. Stir in the salt, pepper and heavy cream.
Using your potato masher, give the soup some texture by mashing - you can do this right in the Instant Pot. You don't want to use an immersion blender as you have kale & cabbage in there.
Taste test - need more salt? Add it - same with pepper.
Ladle into bowls - mix in some sliced green onions if you wish.