How to Make It
Preheat the oven to 400°. Brush the leeks with the olive oil, season with salt and pepper and place cut side down in a 9-by-13-inch baking dish. Add 2 tablespoons of water to the dish, cover tightly with aluminum foil and bake for 20 minutes until tender. Uncover and continue roasting the leeks for 10 minutes until caramelized. Let cool slightly, then coarsely chop and set aside.
Clean out the baking dish and spray with vegetable oil spray.
In a large bowl, toss the roasted leeks with the cannellini beans, garlic, lemon zest, chicken broth and 1/4 cup parsley and season with salt and pepper. Spoon the leek-and-bean mixture into the prepared baking dish. Top with the Gruyère cheese and bake for 15 minutes, until bubbly around the edges and browned on top. Garnish with parsley and serve.
Tip: Any leftover gratin can be mashed and served as a dip or spread for toasts. One serving: 309 cal, 10 gm fat, 3 gm sat fat, 40 gm carb, 11 gm fiber, 16 gm protein.