The trick to getting a rich creamy soup is to use parts of the chicken that have a lot of collagen and fat, cooking them long enough to allow the collagen to break down into gelatin, and then emulsifying the fat into the stock.
The best parts of the chicken for their combination of skin, cartilage and well exercised meat are the wing tips. This is the part you usually use as a handle when you're chowing down on buffalo wings. My butcher happens to separate the wing tips from the meaty part of the wing, so I can pick up a big bag of them for about a dollar. If you ask around and can't find anyone to sell you just the wing tips, whole chicken wings will work as well (your stock will just be a lot more expensive)
While the wing tips have a ton of skin and collagen, they don't have much in the way of bones, which is why I like to use a 50/50 mix of wing tips and other chicken bones (leg bones, carcases, etc). This gives you the best of both worlds, in that you get a rich creamy texture from the wing tips and full-bodied chicken flavor from the larger bones.
Instead, I start by scrubbing away as much blood as I can before cooking the bones, and then diligently scoop off the brown foam that floats to the surface. The foam is created by the proteins in the blood coagulating and will not only give you stock an off-flavor, it will turn the soup brown unless it's removed.
As for aromatics, what you add depends on the kind of stock you want to make. If you want a standard stock, try celery greens, carrots, onions, bay leaves, and black pepper. If you want a ramen stock, fry some garlic, ginger and scallion whites until nearly burned. If you want to go for something more southeast asian, shallots, lemongrass, galangal, garlic and star anise make a great combo.
- Clean your chicken well, under cold running water. Focus on the cut surfaces and if you see blood coming out, squeeze the muscle tissue around the area to coax out any blood remaining in the meat. If you are using whole carcasses, use a spoon to scrape out all the dark organ bits inside the carcass, especially along the spine and ribs. Your chicken should be as clean and blood-free on the inside as it is on the outside.
- In a 7-10 quart pressure cooker, add the chicken and water and bring it to a rolling boil. Use a skimmer to scrape away the foam that accumulates on the surface. Keep skimming until there's no more foam coming to the surface.
- When the stock is clean, add your aromatics and turn the heat off.
- Secure the lid to the pressure cooker and then turn the heat back on high. Let the cooker come up to pressure (it will start whistling) and then turn the heat progressively down until you hear a slow gentle whistle. If the whistling stops after a while, turn the heat back up slightly. Set a timer for 1 hour.
- After the chicken cooks for an hour you can either let the pressure drop naturally or opt for one of the quick release methods for your particular cooker.
- After the pressure drops and you open up the cooker, use a large whisk to whisk chicken stock, breaking up the chunks into a pulp. This does two things. The first is that it breaks up any clumps of gelatin (formerly skin and cartilage) and dissolves them into the soup. The second thing is that the whisking will emulsify the fat into the stock. This is what gives your soup its thick luscious texture and creamy taste.
- After you're done whisking, pass the stock through a colander into another pot or large bowl, then press on the solids with the back of a ladle to squeeze out as much flavor as you can from the pulp.
- Discard the solids, then either wash out the original pot or prepare some containers to store your stock. Use a fine mesh (double mesh) sieve to strain your stock once again and store until you're ready to use.
- The stock will solidify in the refrigerator, this is the collagen (a.k.a. gelatin) at work and means you made a good stock. You'll also notice a layer of yellow fat with a thinner creamy white layer between the fat and the stock. You can scrape some of the yellow fat off and use it for something else, but don't scrape off all of it, and be sure to leave behind the thin layer of white stuff between the yellow fat and the stock.
- To melt the stock, just reheat it and use a whisk to emulsify the fat back into the stock.