Peel and wash the potatoes and cut them into thin slices. Cook in salted water for about 10 minutes
Heat the fat. Sweat flour and tomato paste in it. Stir in wine, 1/4 l water and stock. Simmer for about 5 minutes, season
Peel and chop the shallots. Wash and chop the herbs. Mix both. Wash fillets, dab dry, cut in half lengthwise. Sprinkle with lemon juice, salt
Spread the fillets with mustard and add 2/3 of the herb mixture. Roll up the fillets, pin them down
Wash the crabs, dab them. Drain the potatoes. Put them in a greased casserole dish. Put the rolls and prawns on top. Pour sauce over them. Sprinkle the rest of the herb mixture over the potatoes. Cook in a hot oven (electric cooker: 200 °C/ convection oven: 175 °C/gas: level 3) for 25-30 minutes