Cold water the clay pot with the lid for about 15 minutes, then remove it. Peel garlic and onions. Finely chop the garlic. Halve and slice the onions. Clean, wash and chop the vegetables.
Wash the rosemary, pluck the needles and chop. Wash the meat, dab dry and season. Fill vegetables, onions, rosemary and half of the garlic into the clay pot, mix and season with salt and pepper.
Place the fillets on top. Put the lid on the pot. Put it in the cold oven. Cook in the non-preheated oven (electric cooker: 200 °C/ gas: level 3) for about 1 1/4 hours. Wash the lemon hot and rub dry.
Finely grate the skin, squeeze the juice. Wash parsley, dab dry and chop finely. Mix lemon zest, parsley and the rest of the garlic. Dissolve stock in 1/8 litre hot water, stir in tomato paste and pour on after 50 minutes cooking time.
Sprinkle lemon mixture over it. Finish cooking in an open pot. Season to taste with salt, pepper and some lemon. Garnish with lemon spirals as desired. Wholemeal bread tastes good with it.