Place the chicken / turkey carcass/es / bones in a large cooking pot which has a lid.
Roughly chop all the vegetables. Don’t worry about peeling, just make sure they are washed and clean. Place them in the pot along with the bones.
Add the herbs, salt (if you are using) and pepper into the pot.
Fill the cooking pot up with water. If you are in the UK then tap water is fine. You can take your pot over to the tap to fill up directly. The water should cover the bones and the vegetables but make sure there is decent headroom to the top of the pot so it won’t boil over.
Place the cooking pot on the stove and heat over a medium-high heat. As soon as the water reaches a gentle simmer then turn the heat down so the liquid stays at a simmer. Place the lid on and cook for 2 hours (chicken) or 4 hours (turkey). Check on the progress every so often.
After the allotted time then turn off the heat. Allow to sit for a moment whilst you prepare the ice bath to cool the stock. You will need a large deep casserole dish / crockpot (you could use the sink but I find the casserole dish easier to keep cold as it’s smaller). Fill halfway up with ice then top up with a little cold water.
Strain the stock into a large container with a pourable spout. You’ll probably need to do this in two / three stages due to how big your container is and how full your sieve is getting.
Pour the sieved stock into food storage bags (if you are planning on storing the stock in the food storage bags you might like to measure the amount you are adding in). Expel the air from the storage bags and seal.
Submerge the bags into your prepared ice water bath. The temperature needs to reduce to 4°C (39°F) within 90 minutes to avoid bacteria forming. It should only take about an hour to get to that temperature so keep checking it with a digital thermometer and replenish the ice every so often to keep it as cold as possible.
Once the stock has cooled then decant into your chosen storage method and place the stock in either the fridge or freezer, depending on which suits your cooking plans.