01 - Place potatoes in a large pot, cover with cold salted water, and bring to a boil. Reduce heat and simmer for 15–18 minutes until fork-tender.
02 - In a separate pot, melt half the butter over medium heat. Add cabbage and cook, stirring, for 5–7 minutes until soft but not browned. Stir in spring onions and cook 1 minute more. Remove from heat.
03 - Drain potatoes well and return to pot. Mash thoroughly until smooth.
04 - Gently heat the milk, then add to potatoes along with remaining butter. Mix until creamy and smooth.
05 - Fold in cooked cabbage and spring onions. Season generously with salt and pepper.
06 - Transfer to a warm serving bowl and top with extra butter melting on top.