Eels are cleaned well, peel and cut into pieces with a length of 10 cm. In the butter fry the grated onion and washed, finely chopped herbs with 1-2 tbsp lemon juice. Top put the pieces eel, seasoned with salt, pepper, thyme and bay leaf. Pour the white wine and stew for 15-20 minutes on low heat. Eel pieces are removed and arranged in bowls or in total plate. Yolk, cream, remaining lemon juice and potato flour, mix thoroughly by placing them on the stove, and beat vigorously with a wire until boiling (it should not boil). The sauce is poured over the pieces eel. All garnished with lemon slices and dusted with parsley. Serve well chilled.