Remove the neck and gizzards from the chicken. Place the neck and the chicken, breast side up, into the pressure cooker and add 2 cups of water. Set aside gizzards. Secure the lid. Cook at high pressure for 25 minutes, and allow for natural pressure release. (If your chicken is over 5 pounds, add a few extra minutes to ensure it cooks all the way through.).
Remove chicken and neck from cooker. Do not remove the liquid! Place chicken in a casserole dish or a deep plate to catch drippings, and allow it to cool enough to touch it.
In the meantime, place the frozen scraps into the hot cooker to begin thawing. You don't have to thaw them ahead of time, the cooker will do that. I just dump the bag, then place the bag right back in the freezer for the next batch.
Take off your rings!
Harvest all meat from chicken for later use. I use three bowls: meat, bones/other good stuff, and skin. When in doubt, put it in the bone-bowl. If you get a little skin in there, that's okay - you'll just skim the fat off later anyway.
I do not use a knife for this process. The meat should just about fall off the bones. If you're having a really hard time, it may not be cooked all the way through. You can see from the pictures that the chicken breasts come off almost whole, and the dark meat just falls into the bowl. There is very little in the third bowl - that's all I'm going to throw away. The rest gets used.
Either freeze or refrigerate the chicken harvested - I usually get 4-5 cups.
Throw away the skins.
Next, I try to chop the bones up as small as possible and place the pieces into the cooker. I have a a good pair of boning shears that make short work of this. The more you can chop up the bones, the more of the gelatin you can release to give your stock that beautiful "jiggle" when it's done. You know you have a beautiful stock when it dances like Jello!
Also, dump any juice that seeped out during the harvesting process back into the cooker.
So now, you have a little bit of liquid, all your veggies, and your chopped up chicken bones. Cut up the gizzards and toss them on top, along with the bay leaves and peppercorns. This is when I usually add a few more celery leaves, and maybe a little extra parsley. (See picture).
Fill to "Max-fill" line with water. Secure the lid, and set the cooker to cook at high pressure for 25 minutes, then allow for natural release. It will take a while to come up to pressure because the cooker is so full.
Place 2 layers of cheesecloth over a strainer and place the strainer over a LARGE bowl. VERY carefully, pour the contents of the cooker into the strainer, allowing the liquid to run through.
Allow the solids to cool to the touch, then gather the ends of the cheesecloth and press/squeeze as much liquid as you can out of the solids. I shift the solids around and squeeze again a couple times to get as much out as possible.
Some people like to skim the fat off while it is still liquid. I don't. I think that's too much work. I'd rather peel it off in chunks after refrigerating, when it is hard.
Please, please make sure you're practicing safe food prep - you can't just stick the bowl of steaming hot chicken stock into the fridge and think that the temp will come down fast enough to prevent the growth of bacteria.
I usually put the bowl into my sink in an ice bath, and every few minutes, I *gently* stir the stock. After the temp has come down, I'll move it to the fridge overnight.
In the morning, scrape off the congealed fat that has risen to the top. Watch that stock jiggle! Divide into freezable containers in various sizes and freeze until needed.