In a food processor, chop the onion, celery, and carrots together until finely chopped (but not minced).
Stir in vegetable stock, bay leaf, and parsley. Raise the heat to medium-high heat and bring to a boil. As soon as it reaches a boil, lower the heat to a low heat, cover and cook until all the stock has been absorbed by the rice and the rice is tender, about 15 to 18 minutes.
Remove from the heat and let it set for 5 minutes. Discard the bay leaf. Fluff the rice and serve.