Turn the oven on to 392°F (200 °C).
Cut the stalks of the leeks in 2, cut the thick part finely.
Pour the oil in a tray and put it on the stove to heat up. Add the finely chopped leeks and braise until softened. Add the washed rice and tomatoes and leave to simmer for 4-5 min. Pour on 4 cups water, add 1 tbsp vegetable spice, sprinkle celery and black pepper, salt it just a little because the olives contain plenty of salt.
Put the dish in the oven and in the meantime cut the thin part of the leeks into 1″ (2.5 cm) pieces. 10 min. after placing the dish in the oven, take it out, arrange the pieces of leeks and olives, press them with your fingers so they sink into the semi-boiled rice.
Return the dish to the oven and bake until the rice is ready and the leeks turn golden on top.