Flecks of red potato skin and deep green from the winter greens add festive color to the plate.
Remove tough fibrous stems and any wilted or yellow leaves from greens. Wash leaves well and cut into 1-inch pieces. Set aside.
Cook potatoes in a large saucepan of boiling salted water until tender, about 15 minutes. Remove with a slotted spoon and transfer to a medium bowl. Crush with a potato masher or the back of a large spoon and set aside. Add the greens to the boiling water and cook until tender, 2 to 3 minutes. Drain and set aside.
Dry the pot, add oil and heat over medium heat. Add garlic and saute until fragrant, about 1 minute. Add the cooked greens and toss with the garlic. Stir in the crushed potatoes and buttermilk. Season with salt and pepper.
Make Ahead Tip: Prepare up to 1 hour ahead and keep warm over a larger pan of barely simmering water.
1 starch, 1/2 vegetable