Potato and Sweet Potato Torte

Set oven rack at the lowest level; preheat to 450! F. Lightly oil a 9-inch deep-dish pie plate (6-cup capacity) or coat it with vegetable oil spray. Line the bottom with parchmentpaper or aluminum foil. Lightly coat the paper or foil with oil or cooking spray. Heat oil in a large nonstick skillet over medium-high heat. Add leeks and thyme and saute until tender, about 5 minutes. (If necessary, add 1 to 2 tablespoons water to prevent scorching.) Season with salt and pepper. Arrange half of the sweet potato slices, slightly overlapping, in the bottom of the prepared pie plate and season with salt and pepper. Spread one-third of the leek mixture over the top. Arrange half of the all-purpose potato slices third of the leeks. Layer remaining sweet potatoes, leeks and all purpose potatoes in the same manner. Cover the pie plate tightly with aluminum foil and bake about 45 minutes, or until the vegetables are tender. (The torte can be prepared ahead and stored, covered, in the refrigerator for up to 2 days. Reheat, covered, in a moderate oven.) Run a knife around the edge of the torte to loosen it. Invert onto a serving plate. Remove paper or foil liner and serve. Makes 6 servings.