01 - Place potatoes in a large pot and cover with cold, salted water. Bring to a boil over high heat, then reduce to simmer. Cook until fork-tender, about 15–20 minutes.
02 - Melt 2 tablespoons butter in a large skillet over medium heat. Add kale and sauté for 3–4 minutes until wilted. Add scallions and garlic, cook for 1 minute more. Remove from heat.
03 - Drain potatoes well and return to pot. Add remaining 2 tablespoons butter and mash until smooth.
04 - Gradually stir in warm milk, mixing until creamy and smooth.
05 - Fold in sautéed kale and scallion mixture. Season generously with salt and pepper.
06 - Serve hot, with an extra pat of butter on top if desired.