01 - Place the potatoes in a large pot and cover with cold, salted water. Bring to a boil, reduce heat, and simmer for 15–20 minutes until fork-tender.
02 - While the potatoes cook, melt 2 tablespoons of butter in a skillet over medium heat. Add the shredded cabbage and sauté for 5–7 minutes until softened but not browned. Stir in the scallions and cook for another 1–2 minutes. Remove from heat.
03 - Drain the potatoes well and return to the pot. Allow them to sit for 1 minute to steam dry.
04 - Mash the potatoes thoroughly using a masher or ricer.
05 - Gently heat the milk and remaining butter in a small saucepan until the butter is melted.
06 - Pour the warm milk mixture into the potatoes and mash until smooth and creamy.
07 - Fold in the sautéed cabbage and scallions. Season generously with salt and pepper.
08 - Transfer to a serving bowl and top with a few extra knobs of butter, allowing them to melt over the hot mash.