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