Step 1

Place potatoes and 1 tablespoon salt in large saucepan, add water to cover by 1 inch, and bring to boil over high heat. Reduce heat to medium and simmer until potatoes are tender and paring knife can be easily slipped in and out of potatoes, 18 to 22 minutes.

Step 2

Meanwhile, stem kale, then slice stems thin crosswise and set aside. Cut leaves into 1-inch pieces. Melt 6 tablespoons butter in 12-inch skillet over medium heat. Add kale stems, 1 tablespoon water, salt, and pepper. Cook, stirring occasionally, until kale stems have softened, 6 to 8 minutes. Stir in kale leaves and scallions, and cook until kale leaves have wilted and scallions are softened, 1 to 2 minutes. Stir in milk, increase heat to high, and bring to simmer. Remove pan from heat and cover to keep warm.

Step 3

Drain potatoes and return to saucepan. Cook over low heat, stirring, until potatoes are thoroughly dried, about 30 seconds. Remove from heat. Pour milk mixture through fine-mesh strainer over potatoes; reserve solids. Using potato masher, mash potatoes to desired smoothness. Gently fold in solids from strainer. Season with salt and pepper to taste.

Step 4

Transfer potatoes to serving bowl. Using spoon, create depression in center of potatoes. Place remaining 2 tablespoons butter in depression. Serve.