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