Ingredients

1. Kosher salt
2. 5 1/2 pounds mixed bitter greens, such as Swiss chard, escarole, turnip or mustard greens, chicory, broccoli rabe, kale and spinach, tough stems discarded
3. 1 stick (4 ounces) unsalted butter
4. 4 large leeks, white and tender green, thinly sliced crosswise
5. 2 garlic cloves, thinly sliced
6. 3 cups chicken stock, fresh or canned low-sodium broth
7. Freshly ground pepper
8. 3 pounds Yukon Gold potatoes

Directions

1. Bring a large pot of water to a boil and add salt. Cut the greens into 1-inch pieces and wash them thoroughly. Add the greens to the pot and cover. As soon as the water returns to a boil, drain the greens in a colander; pat dry.
2. Preheat the oven to 375°. In a large skillet, melt 4 tablespoons of the butter. Add the leeks and garlic and cook over moderate heat until just beginning to brown, about 10 minutes. Add the Chicken Stock and bring to a boil. Season generously with salt and pepper and remove from the heat. 
3. Peel and halve the potatoes and slice them 1/4 inch thick. In a large bowl, toss the potatoes with the greens and leeks. Season with salt and pepper. Transfer the mixture to a large nonreactive baking dish and press the vegetables down firmly. Dot with the remaining 4 tablespoons of butter. Cover the pan tightly with foil and bake for 1 hour. Uncover and bake for about 15 minutes longer, or until the potatoes are very tender. 
4.  

Make Ahead

This dish can be prepared early in the day and reheated in the oven.