01 - Place potatoes in a large pot and cover with cold water. Add 1 teaspoon salt. Bring to a boil, then reduce heat and simmer for 15-20 minutes until fork-tender.
02 - Melt 2 tablespoons butter in a large skillet over medium heat. Add cabbage and sauté for 5-7 minutes until soft but not browned. Stir in scallions and cook for 2 minutes more, then remove from heat.
03 - Drain potatoes well and return to pot. Add remaining 2 tablespoons butter and mash until smooth.
04 - Gradually stir in hot milk until potatoes are creamy and fluffy.
05 - Fold in sautéed cabbage and scallions. Season with salt and pepper to taste.
06 - Serve hot with a generous pat of butter melting on top.