In a food processor, chop the onion, celery, and carrots together until finely chopped (but not minced).
Heat the olive oil in a medium saucepan over medium heat. Add the chopped vegetables, season with the salt & pepper and cook until soft, about 5 - 7 minutes.
Add the rice and stir until coated.
Increase the heat to medium-high.
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.
* This recipe calls for parboiled or converted rice. In the US, look for Uncle Bens Converted Rice, or Golden Canilla Parboiled Rice. In the UK, buy Uncle Bens Long Grain Rice (not quick cook).
Substituting The RiceYou can use other types of long-grain rice (although I don't recommend instant, quick-cook, or brown rice). Just be sure to consult the package instructions for the rice to liquid ratios and cooking times and adjust accordingly.