Wash your potatoes, peel them, and use the potatoes as you had planned to use them anyway.
Put the peelings into your pressure cooker along with a bay leaf or two, and a few cloves of garlic. No need to salt or season further -- in fact, it's best if you don't, for maximum flexibility later.
Use enough water to cover the peelings, then about 500 ml (2 cups) more. Remember, it's best to keep the stock concentrated so that it takes up less room in the freezer -- why dilute with tons of water that will just take up freezer space.
Ready to cook
About 10 minutes in the pressure cooker should be enough time.
10 minutes should be enough
At the end of cooking, just pour it all through a strainer, then put in a covered container or a freezer bag, and freeze!
Drain, and freeze
The healthiest part of a potato is its peel, and you've just extracted a truckload of nutrients from it into a rich stock that will give a taste and nutrition kickstart to many future items you make! For free!
Notes
Sometimes the stock will come out darker than other times -- it depends upon the variety of potato.