Instructions

1. Place 1 pound chopped russet potatoes and 1 pound chopped red potatoes and 1/2 teaspoon of the kosher salt in a medium pot and cover with cool water. Bring to a simmer over high heat. Reduce the heat as needed to maintain a simmer and cook until the potatoes are tender, 10 to 12 minutes. Meanwhile, brown the butter.
2. Melt 6 tablespoons unsalted butter in a 12-inch skillet (preferable something with a lightly colored interior) over medium-high heat. Bring the butter to a simmer and cook until it browns and smells nutty, about 7 minutes. Pour off 1/4 cup of the browned butter into a small heatproof bowl and set aside.
3. Return the pan with the remaining browned butter to medium heat and add 1 small head shredded savoy cabbage and the whites of 4 medium scallions. The pan will be quite full, but the cabbage will wilt, making stirring easier. Season with the remaining 1/2 teaspoon kosher salt and 1/2 teaspoon black pepper. Cook until tender and lightly browned, about 8 minutes.
4. Drain the potatoes and return them to the cooking pot. Add 1/2 cup whole milk and mash with a potato masher. The potatoes should retain a few small lumps for texture.
5. Add 1/4 cup low-sodium chicken broth to the cabbage pan and scrape vigorously to remove any browned bits from the bottom of the pan. Cook until the broth is reduced, about 3 minutes more.
6. Add the cabbage and any remaining liquid, plus the greens of the green onions, to the mashed potatoes and fold to combine. Taste and season with more kosher salt as needed. Transfer the colcannon to a large serving bowl and make a well in the middle of the potatoes. Pour the reserved 1/4 cup brown butter into the well and serve immediately.