Add 2 cups of water to the inner pot. Place the whole potatoes in the basket or on the rack of your pressure cooker. Place the pressure lid on and turn the valve to seal. Pressure cook on high for 30 minutes (see times in notes for various potato sizes). When the time is up immediately release the pressure.
While the potatoes are pressure cooking, slice the cabbage into thin strips, about ¼", until you have 1 cup. Slice the leek into ¼" rounds, using both the white end and the dark green end until you have 1 cup. Slice the green onion into ¼" pieces and put in a separate bowl.
Melt the butter (I keep out 2 Tbsp of the butter to put on top before serving) and add the cream. When the PC time is up, remove the lid and place the potatoes on a cutting board.
No need to change the water, just add the vegetables to the basket and put the pressure lid on. Turn the valve to vent and steam for 3 minutes. If you are using a brand of pressure cooker that seals the pot on the steam function like many IPs do, then decrease the time to 2 minutes. When the time is up and the pin has dropped, open the lid so the vegetables don't over cook.
While the vegetables are steaming, peel the potatoes by holding one with a fork and use a spoon to scrape the skin off. Place the peeled whole potatoes in a bowl large enough for mashing.
Add salt and half of the butter/cream mixture and mash using a hand mixer or by hand using a potato masher. I used the Mix 'N Chop from Pampered Chef and it works great. Add as much of the remaining cream/butter mixture as needed to get the desired consistency. I used all of it in all of my test batches.
Add the steamed leeks and cabbage on top and mix to combine. Add the raw green onions and mix. Place the pat of butter on top. Serve & Enjoy!