Check off each step as you cook.

1. 01Start the vegetable topping.Heat half the oil in a broad saucepan over medium-low heat. Cook onion for 5–6 minutes. Add carrot, parsnip, and celery root and cook for about 8 minutes, stirring often. Stir in tomato paste for 1 minute.
2. 02Simmer until tender.Add stock, bay leaves, allspice, sugar, and half the salt. Cover and simmer gently for 15–20 minutes, stirring occasionally, until the vegetables are tender but not mushy. Uncover briefly if very wet. Remove bay leaves and allspice, then stir in lemon juice.
3. 03Cook the fish.While the vegetables simmer, pat fish dry and cut into broad serving pieces. Season with the remaining salt and pepper, then coat lightly in flour, shaking off excess. Heat the remaining oil in a skillet over medium heat and fry in batches for about 3–4 minutes per side, depending on thickness, until the center reaches 145°F / 63°C and flakes easily.
4. 04Layer and cool promptly.Spread a little vegetable mixture in a shallow food-safe container. Add the fish in a loose single layer, then cover with the remaining vegetables. Set the container in a cool-water bath for about 20 minutes, keeping water out of the food, until it is no longer hot.
5. 05Chill before serving.Cover and refrigerate for at least 2 hours until thoroughly cold. Lift portions gently onto plates and spoon over the vegetable topping.

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