01 - Place potatoes in a large saucepan, cover with cold salted water, and bring to a boil. Reduce heat and simmer for 15-20 minutes until fork-tender.
02 - Bring a second pot of salted water to a boil. Add shredded cabbage and cook for 4-5 minutes until just tender. Drain well.
03 - In a small saucepan, gently heat milk and butter together until butter melts. Do not boil.
04 - Drain potatoes thoroughly and return to pot. Mash until smooth and fluffy.
05 - Gradually stir warm milk and butter mixture into mashed potatoes, then fold in drained cabbage and sliced scallions. Season with salt and pepper to taste.
06 - Serve immediately with extra butter on top if desired.