Tonight when I was getting ready to make chicken soup, I realized I didn't have enough stock in the freezer. Not a problem!
Typically, the stock I make takes about 8 hours, but if you don't have the time you can just throw a couple of chicken breasts (boneless, skinless) in a pot and cover them with water. Add a stock of celery and a medium size carrot, both broken into quarters, and then half an onion, also quartered (I don't even peel the carrot or remove the onion skin -- just give everything a good wash). Finally, add a bay leaf and salt to taste. Bring to a boil and simmer for half an hour. Remove the chicken and vegetables. Set aside the chicken for shredding and discard the vegetables. Strain the broth through a fine mesh strainer and there is the base for your soup!
If you like a bit more concentrated flavor, let the stock (with everything in it) go a little longer to reduce.