Bring the potatoes to the boil, then simmer for 15-20 minutes or until completely tender.
In the meantime, warm a sauté pan, over medium heat, add half of the butter and add the cabbage, add a dash of vegetable stock or water. Season well.
Sauté for 2-3 minutes until softened. remove from the heat.
Once the potatoes are tender, remove from the heat and drain in a colander.
Return to the saucepan.
Add the rest of the butter and buttermilk and mash using a potato masher.
Add the cooked cabbage and check the seasoning.
Serve piping hot.