Put chicken thighs in a large pot, covering with enough water to be about 2" above chicken, add onion, celery, soup base and bay leaf. Bring to a boil, reduce heat to a low simmer, cover with a tilted lid and cook til meat is almost ready to fall off the bone, about an hour. Remove chicken from pot to a plate to cool, and with a slotted spoon remove onion, celery and bay leaf, making sure to thoroughly skim stock for any bones, etc. Discard veggies. Bring your stock back to a low simmer. Mix Bisquick with milk and add parsley to stock. Using the 2-spoon method, GENTLY drop golf ball size balls of dough into broth, until all dough is in the pot. DO NOT STIR. Stiring dumplings is what causes them to be chewy doughballs instead of fluffy bread pillows. Again, cover with a tilted lid and gently simmer for about 25 minutes, and don't touch them. While they are cooking, debone your chicken. Check for doneness on dumplings with a toothpick the same way you would a cake...if it comes out clean, they are done. Add salt and pepper and chicken meat, still not stirring, just gently push the meat down into the broth and then slosh the pot around. Serve hot, even better the next day.