Chop the potatoes, cabbage (or kale) and onion (or scallions).
In a medium pot, add the potatoes and cover with cold water. Bring to boil over medium-high heat and continue to boil until potatoes are tender when pierced with a fork (15 minutes). Drain well and return to pot.
While potatoes are boiling, in a separate pot, over medium-high heat the butter.
Cook the greens until slightly tender, about 6-7 minutes.
Add the milk and remaining butter to the potatoes and mash with a potato masher, fork or use mixer.
Now, add the cabbage or kale mixutre, stock, salt and pepper and more butter to taste. Serve hot with a garnish of chopped scallions.