1. Salt the fish inside and out and refrigerate for 1 hour.

2. Meanwhile, prepare the vegetables: Heat the olive oil in a large pot and cook the onions over low heat, stirring until wilted, about 10 minutes. Add the carrots, celery, and celery seeds, if using, and toss to coat with the oil. Season with salt and pepper and pour in half the lemon juice and enough water to cover the vegetables by ½ inch/1,5 cm. Cover and simmer over low heat until the vegetables are tender, about 45 minutes, adding water if necessary to keep the mixture from burning. Place the fish on top of the vegetables in the pot. Cover and simmer until flaky, about 15 minutes.

3. Prepare the egg-lemon sauce: Beat the eggs and remaining lemon juice together with a wire whisk in a small bowl. Slowly add a ladleful of the pan juices from the fish, whisking all the while, and immediately pour the avgolemono into the pot. Stir gently, remove from the heat, and serve.