Ingredients:
1 1/2 pounds potatoes, thinly sliced
1 pound leeks, trimmed, rinsed well, and thinly sliced
1/4 cup olive oil
Salt and black pepper
4 sprigs fresh thyme, or several pinches dried
1 cup bread crumbs (preferably whole grain)
2 tablespoons butter, melted.
Directions:
1. Heat the oven to 375 F. Put the potatoes and leeks in a large (9 x 13 or 3 quart) baking dish and toss them well with the oil. Sprinkle with salt and pepper and nestle the thyme sprigs among them (or sprinkle with dried thyme). Cover the baking dish with foil and bake until the vegetables are just tender, 30 to 40 minutes. Remove the dish from the oven, uncover, and raise the oven temperature to 425 F. (Note: You can make the gratin ahead to this point. Leave covered and refrigerate for up to a day; bring to room temperature before proceeding.)
2. Toss the bread crumbs with the melted butter, sprinkle them over the vegetables, press down a bit, and return the pan to the oven. Bake until the bread crumbs and vegetables are nicely browned, 15 to 20 minutes more. Serve hot or at room temperature.