How to Make It
In a blender, combine the parsley, egg, vinegar and oil and puree. Season with salt.
In a medium saucepan, combine the water, butter and a large pinch of salt and bring to a boil. Add the cabbage leaves, cover and simmer over moderate heat, stirring occasionally, until tender, about 4 minutes. Drain the cabbage leaves and pat dry.
Tightly roll up the leaves and arrange the rolls on plates. Season lightly with salt and top with the parsley sauce. Garnish with the scallions and sprouts and serve right away with rye crisps.