01 - Place 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 - Melt 2 tbsp butter in a large skillet over medium heat. Add chopped kale and cook for 4-5 minutes until tender and bright green. Stir in scallions and cook 1 minute longer.
03 - Drain potatoes well and return to pot. Add milk and remaining 2 tbsp butter. Mash until smooth and creamy.
04 - Fold sautéed kale and scallions into mashed potatoes. Season generously with salt and pepper.
05 - Transfer to serving bowl and make a small well in center. Add extra knob of butter to melt on top before serving.