Wash the sardines and chop the heads of them. Then open them up, empty them out and take away the bones. Afterwards, wash them well again and drain them.
In a little of the butter, brown the cleaned, peeled and finely sliced mushrooms. Soak the fresh breadcrumbs in the milk, then strain them, next add the finely chopped fresh herbs. Make a paste with these three ingredients and add to the mixture the egg yolks, the cream, the lemon juice and the herbs, blending them together well.
Fill the sardines with this mixture and close them again. Then plunge them, one by one, into the whisked egg whites and roll them in the dry breadcrumbs. Arrange them in a well-greased baking tin, soak them with the white wine and put them in a preheated oven at 200°C/400°F for a few minutes.
Arrange them afterwards on a serving dish, pour over the cooking juices which have been mixed with the butter and sprinkle with parsley. Add some salt and serve with wedges of the lemons.