Rinse the fish slices, dry them and sprinkle with a small amount of juice from one lemon. Briefly soak the capers, drain and chop coarsely. Peel the cucumber, cut in half, scrape out the seeds with a spoon and cut the halves into small cubes.
Heat butter or possibly light butter in a casserole and sauté the carrots in it. Cover with water and cook.
Add the diced cucumber, season with salt and cayenne pepper. Finely chop the parsley and stir in at the end. Preheat the oven to 180 °C.
Boil the fish stock and white wine to 1/3. Remove from the heat, add the remaining juice of one lemon and gradually whisk eight tablespoons of olive oil into the sauce with a hand mixer. Stir in the capers and season with cayenne pepper and salt.
Heat the remaining olive oil in a large casserole, pour in the fish slices and cook in the hot oven, turning, for five to six minutes.
Tip: Do you know purple carrots? They are an old, very aromatic variety – why not use them for a change!