Place the peeled and chunked potatoes in a large pot and cover with cold, salted water by at least an inch. Bring to a boil over high heat, then reduce heat to medium and simmer for 15-20 minutes, or until the potatoes are easily pierced with a fork.

While the potatoes are cooking, melt 2 tablespoons of the butter in a large skillet over medium heat. Add the shredded cabbage and cook, stirring frequently, for 5-7 minutes until it has wilted and become tender.

Drain the cooked potatoes thoroughly in a colander. Return the empty pot to the stove over low heat for one minute to evaporate any remaining moisture. Return the potatoes to the dry pot and mash them until smooth with a potato masher or press them through a ricer.

Gently warm the heavy cream and the remaining 6 tablespoons of butter in a small saucepan or in the microwave. Pour the warm cream mixture into the mashed potatoes and stir gently until just combined. Be careful not to overmix.

Fold the sautéed cabbage and the sliced green onions into the potato mixture. Season generously with salt and pepper. Serve immediately, making a well in the center and adding an extra pat of butter if desired.