Defrost frozen crayfish tails. Clean, wash and drain the leek. Cut off approx. 50 g of the white leek and dice finely. Cut the remaining leek into rings.
Prepare the pasta with the leek rings in boiling salted water according to the instructions on the packet. Rinse crayfish and pat dry. Heat the fat in a pan. Fry the crayfish lightly in it. Finally add the leek cubes, steam briefly and deglaze with wine and cream.
Bring to the boil and simmer for 1-2 minutes. Add the sauce thickener and bring to the boil again briefly while stirring. Season sauce with salt, pepper and sugar. Drain the noodle-leek mixture and let it drain.
Grease 8 mussel shells or an ovenproof dish. Add the pasta, spread the sauce over it and sprinkle with cheese. Gratinate under the preheated grill for approx. 5 minutes or bake in the preheated oven (electric cooker: 225 °C/ convection oven: 200 °C/ gas: level 4) for approx. 10 minutes.