Super-cheesy and super-creamy, this side deserves a spot on your holiday table.
Preheat the oven to 400°. Grease a 3-quart baking dish. Bring a large pot of water to a boil. Salt the water and add the kale. Cook, stirring occasionally, until wilted and tender, 2 to 3 minutes. Drain, then rinse under cold water to cool. Squeeze the kale until very dry; coarsely chop.
In a large pot, melt the butter over medium-high heat. Add the onion; season with 1 tsp. salt and 1/2 tsp. pepper. Cook, stirring often, until soft, about 5 minutes. Mix in the kale and thyme. Add the cream and nutmeg. Bring to a boil. Stir in half the cheese. Mix in the potatoes.
Transfer the potatoes and kale to the baking dish. Top with the remaining cheese. Cover with foil, tenting the foil in the center to prevent it from sticking to the cheese. Bake for 30 minutes. Uncover and bake until the top is bubbly and browned in spots, about 20 minutes more. Let rest for 15 minutes before serving.
Get the full 8-person holiday dinner menu