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, approximately 15-20 minutes.
02 - While potatoes cook, 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, cooking 1 additional minute. Remove from heat.
03 - Drain potatoes thoroughly and return to pot. Add remaining 2 tablespoons butter and mash until smooth.
04 - Gradually stir warm milk into mashed potatoes, mixing until creamy and smooth consistency is achieved.
05 - Fold sautéed kale and scallion mixture into mashed potatoes. Season generously with salt and freshly ground black pepper.
06 - Serve hot, topped with an extra pat of butter if desired.