Carefully clean leeks, cut away root end, rinse and cut into tender strips. Bring salted water to the boil. Pour in leeks and blanch for just one minute. Drain and drain well.
Stir butter with a ladle until peaks form. Season with salt, cayenne pepper and juice of one lemon. Remove crust from toast and chop very finely. Stir into a paste with one-third of the precooked leeks and the lemon butter.
Season fish fillets lightly with salt and brush with the leek butter. Place in a baking dish and pour the white wine around them. Place the cod fillets in the middle of the oven heated to 230 degrees and bake under the broiler for 6-8 minutes until a light crust has formed.
At the same time put the remaining leek with the cream in a frying pan, make about three min. and season with salt as well as pepper. Put the leek vegetables on warmed plates and arrange the fish fillets on them.