Peel and wash the potatoes and cook them in boiling salted water for about 20 minutes. Peel and clean the carrots and quarter them lengthwise. Wash fish, dab dry. Peel and halve the onion.
Bring laurel, vinegar, 250 ml stock, wine, 300 ml water and onion to the boil. Season with salt. Put the fish into the stock and cook at about 80 °C for about 10 minutes. Melt the fat, add the carrots, pour on 100 ml stock, bring to the boil and stew for about 5 minutes.
Season with salt. Measure out 100 ml fish stock and boil down to half of it for about 5 minutes. Add cream. Season to taste with salt and pepper. Arrange carrots, potatoes, fish and sauce on plates. Garnish with parsley.