Wash (or peel) carrots and celery. Slice into 1-inch bite sized pieces.
Remove skins from chicken thighs and trim any excess fat. If your local grocery store carries skinless thighs, they are often less expensive. Worth checking out…
Chop onion roughly.
Set pressure cooker over medium heat and melt butter. Once warm, add onions and cook until soft. About 5 minutes.
Add the water, carrots, celery, bay leaves, and thyme. NO SALT yet, this will kill your meat texture!
Prepare your pressure cooker lid by giving the seal a quick rub with oil.
Increase heat to medium-high, and bring to a boil. Once boiling, gently add the chicken thighs and lock the lid in place. Set to high pressure (setting #2 on the Fagor or about 15 lbs) and once it starts whistling, reduce heat to medium-low maintaining a gentle hiss from the lid.
Cook for 15 minutes once pressure is achieved.
Use the quick-release method to stop the chicken cooking. This is done by taking the pressure cooker to the sink and running cold water over the outside. You will see the pressure releases fast!Once the safety indicator has fallen, i.e. pressure is released, return pan to the stovetop and open carefully. Tilt the lid away from your face because there will still be some really hot steam!
With a slotted spoon or tongs, remove the chicken thighs to a plate and allow to cool. Set pot over medium heat and return soup to a gentle simmer.
Once the chicken is cool enough to handle, strip the meat off of the bones and shred into bite sized pieces with your fingers. It will be super tender, so no need to break it up too much or you will not be able to find the pieces.
Add spinach to soup and cook for about 2 minutes. Return chicken to pot and cook very briefly, about 1-2 minutes at a gentle simmer. It’s plenty cooked already, we just want to warm it back up!
Kill the heat and add the lemon juice. Whoaaa chemistry… The soup will become a luxurious white opaque color. Adjust salt and pepper to taste.