Heat oil in a large saucepan over medium heat.
Add celery, carrots and onions and cook, stirring, until starting to soften, about 2 minutes.
Add mushrooms and cook, stirring, until the mushroom liquid has mostly evaporated, about 5 minutes.
Add flour, pepper and salt and cook, stirring, for 2 minutes more.
Add broth and bring to a boil, scraping up any browned bits.
Cook, stirring, until slightly thickened, about 2 minutes.
Stir in rice, cream, lemon juice and parsley and cook until heated through, about 2 minutes more.
