In your pressure cooker or a Dutch oven, place the chicken, boxed stock, onion and peppercorns. Bring up to pressure and cook at high pressure for 15 minutes. (If using a Dutch oven, simmer over medium-low heat until the chicken is cooked through. You may have to flip the chicken to get it to cook evenly).
Carefully remove all the meat from the carcass and set aside to cool. Refrigerate after it has cooled off some, about 30 minutes.
Return the carcass to the pot. Add enough additional water to almost cover the chicken.
Put the lid on the pressure cooker and cook at high pressure for 1 hour to produce a lovely stock. (If using a Dutch oven, this will take 3-4 hours at least. You can skip this step entirely if you want and just use some extra boxed stock).
Strain the stock into another pot, pressing down on the solids.
Skim off as much of the fat as you want. I probably ended up skimming off about 1/4 cup of fat. Save this. It's schmalz, and it's gold.
Add the flour slurry to the stock along with the poultry seasoning. Bring to a boil to thicken the sauce.
Taste and adjust seasonings.
Bring to a very low boil. Drop dumplings (procedure below) into the pot, a few at a time so they don't stick together.
Cover the pot and reduce the heat to maintain a low simmer. Simmer for about 15-20 minutes, or until dumplings are cooked through.
Return the reserved chicken to the pot to reheat.
Serve in bowls with a fork and a spoon. Have some good bread or rolls handy to sop up the extra sauce.
Grin like an idiot and enjoy!