Broth

Ingredients

• Bones. Lots of bones. For pork bones, it's traditional to use thigh bones that have been broken or cut open, to allow the marrow out. Ribs are also used a lot, a long with whole chicken carcasses or just wings and/or feet. If you want to add some seafoody flavors to the broth then you'll need some prawn shells or a lobster tail shell.
• Vegetables. Or vegetable peelings. The usual suspects include your favorite form of mirepoix/soffrito/soffrito/Süppengruns/włoszczyzna/holy trinity, garlic, leeks, peppers, and Japanese green onion (called "negi", which look like regular green onions scaled up 3 times in all directions). Roughly an onion's worth, for scale.
• Unflavored gelatin - while I believe that doing this will make a broth that gels, there's no harm in being certain about that - 2 sachets
• Rendered pork and/or chicken fat - a heaped tablespoon.

Equipment

• A pressure cooker. Something like the Instant Pot branded cookers. Mine does pressure cook and sous-vide functionality and both are used here. I'm going to refer to it as an instant pot as a generic. Mine is 8 quarts.
• Fine mesh sieve
• Blender - ideally a stick style blender

Prep

Whenever you have chicken bones from any source, put them into a bag in the freezer. Raw is fine. Cooked is fine. A rotisserie chicken from the supermarket because you were too lazy to cook and you were already hungry? Also fine. Also save the bits of skin that aren't great to eat in the same bag - you'll get both fat and collagen from that. The gelled juices from the bottom of the container? Definitely save those.

Vegetable peelings and trimmings from the usual suspects and anything else that might be interesting also get frozen in a separate bag, for the same reason.

Method

First Day

If you aren't using pork bones, skip to the second day

Oh yes, this is a multi-day affair.

First, put as many pork thigh bones into the instant pot as you have. Fill to the pressure cooker max line with hot water (boiling is fine), and set for sous-vide cooking. Let it do it's thing for about 20 hours.

Second Day

Remove the pork bones, and use whatever tools you can to remove anything that isn't bone from the bones - marrow, cartilage, tendons, scraps of meat and the like. Return the non-bone material to the broth.

Add your frozen bag of chicken bones, skin, gelled rotisserie drippings, some wings and/or feet if you want to make up volume. Top up with hot water to the pressure cooker maximum fill line if necessary, and set to pressure cook for 90 minutes.

It does not matter whether you quick-release the pressure or allow it to drop naturally. When you open it, mash the bones with a potato masher. They will crush down, leaving you with enough room to add your vegetable peelings, or your mirepoix (-alike), and your seafood shells if you are using them. Pressure cook another 90 minutes.

Straining

The fastest way to strain is with a regular fine-mesh strainer. Pull out the seafood shells and vegetables first, then pour the whole batch through a strainer. You will find an unappetizing brownish sludge gets filtered out.

If you want to do this a second time, you'll get more, and running through cheesecloth gets even more. It will settle to the bottom of its own accord and straining diminishing returns on effort. I strain once, or twice, and not using cheesecloth anymore - I just leave the last of the solids back when I decant.

Ensuring Emulsification and Body

You can do this before straining, if you want. My ordering merely depends on when I remember. Add a couple of sachets of powdered gelatin, and a healing tablespoon of rendered fat from your animal of choice.

Blend. If you had done a natural release and handled everything gently, then you'll see it turn white as you blend and emulsify everything. If you do this before the straining step then it'll turn tan, and turn lighter in color once strained.

Tasting

There is no salt in this broth. To taste it, add a little salt or soy sauce so that you can taste it.

Decant

Decant into containers, allow to cool, and store in the fridge for up to a couple of weeks.