Boil the potatoes in their skins.
Quarter the cabbage, remove the tough stalk and slice thinly across the grain. Rinse the cabbage. Cook the cabbage in a small amount of water and some salt, till just done, retaining some crunch.
When the potatoes are cooked, allow them to cool slightly and remove the skins. Heat the milk to boiling point, gradually add to the potatoes, while mashing to make a fluffy puree.
Mix in an equal volume of cabbage, season with salt and pepper and serve immediatley in a heated dish, making a well at the top for the melting butter