Place peeled, cubed potatoes into a large pot and cover with cold water. Add a pinch of salt. Bring to a boil, then reduce to medium and simmer for 15-20 minutes until fork-tender. Drain and return to the hot pot to steam-dry.

Heat olive oil in a large skillet over medium heat. Add shredded green cabbage and saute for 4-5 minutes until softened. Add the dark green kale ribbons and cook for 2-3 more minutes until tender but bright green.

Warm the milk and half of the butter. Pour over the hot potatoes, adding salt and pepper. Mash with a hand masher until fluffy with a slightly chunky texture. Do not overmix.

Fold the sauteed cabbage and kale into the mashed potatoes until thoroughly mixed. Transfer to a rustic serving bowl and form a mound. Press a deep, circular well in the center.

Melt the remaining butter and pour it into the center well so it pools and slightly drips down the sides. Scatter finely chopped green scallions across the top and serve warm.