Open the sardine cans and pour the oil into a cup.
Cut the leeks into thin slices and finely chop the onions. Sautee both in a large pan using the oil from the sardine cans. Mix in the rice and pour in enough water to cover the mixture. Salt and pepper to taste. Peel the celery root, cut into slices and place on top of the rice in the pan. Cook for approx. 15 minutes. After 13 minutes lay the sardines on top of the celery root slices. Cut the radishes into slices with a potato peeler. Decorate the paella with the radish slices, fennel and thyme blossoms and serve.