01 - Place the potatoes in a large pot and cover with cold salted water. Bring to a boil, then simmer for 15–20 minutes until fork-tender.
02 - While the potatoes cook, melt 3½ tbsp of the butter in a large skillet over medium heat. Add the chopped kale and a pinch of salt. Sauté for 4–5 minutes until wilted and tender. Add the sliced scallions; cook for another 2 minutes. Remove from heat.
03 - Drain the potatoes well and return to the pot. Mash until smooth.
04 - Gently heat the milk until just warm, then stir into the potatoes along with the remaining 3½ tbsp butter. Mix until creamy.
05 - Fold in the sautéed kale and scallions. Season with salt and pepper to taste.
06 - Serve hot, topped with an extra knob of butter if desired.