In a large pot, warm the olive oil over medium-high heat. Add the shallot, leek, salt, and pepper and cook until beginning to soften, about two minutes.
Add rice, stock, water, salt, pepper, and herbs de Provence. If you're using white rice, add the carrot and celery now. If your rice cooks for longer, hold off until later.
Bring to a boil, then reduce heat, cover, and simmer for as long as suggested on the rice packaging. (For white rice, about 20 minutes. For brown and wild rice, about 45 minutes.) With 20 minutes left on the rice cooking time, add the carrot and celery.
While the soup simmers, make the beurre manié. In a small bowl, combine the room-temperature butter and the flour. Use a fork to mash it all together to form a thick paste. Keep going until it looks homogenous, with no dry flour remaining.
When rice is cooked, add turkey, cream (if using), and beurre manié. Stir very well until the beurre manié is fully incorporated.
Raise heat again to bring to a boil. Then reduce heat and simmer, uncovered, for 8 minutes to thicken the soup and cook out the flour. Ladle into bowls and serve.