Throw whole carcass or animal parts into the stock pot or slow cooker. You can include the skin, fat, and bones, which make a rich gravy. The meat or carcass you use should not be seasoned and should be safe for human consumption once cooked.
Fill the pot with water to cover the meat you have in the pot.
Bring to a boil, then turn down to a medium or soft boil. Place the lid of the pot on and let simmer for 2–3 hours, stirring occasionally.
Let cool. Strain so there’s nothing left but the liquid. Portion out the gravy and freeze for a great yet simple topper for your cat’s food.