Optional step: Brown the chicken carcasses in your pressure cooker with 1 tablespoon of oil. This will slightly elevate the flavors and result in a brown stock. Then, add water to deglaze the pot with 1/3 cup of water. Add all ingredients in the pressure cooker. Close lid and cook on Manual at high pressure for 1 hour (the longer the better), then natural release. Open lid. Strain the stock through a colander discarding the solids, and set aside to cool. Let the stock sit in the fridge until the fat rises to the top and form a layer of gel. Then, skim off the fat on the surface. You can use the stock immediately, keep it in the fridge, or freeze it for future use.