ONION AND TOMATO SAUCE:

4 tbsp. extra-virgin olive oil
2 med. onions, halved and thinly sliced
Sea salt and freshly ground white pepper to taste
3 plump fresh garlic cloves, minced
5 med. vine-ripened tomatoes, cored, peeled, seeded, and chopped
1 tbsp. sugar

3 lb. baking potatoes, such as Idaho russets
1 plump fresh garlic clove, halved
2 tbsp. unsalted butter, melted
1 1/2 c. chicken stock
1/2 c. fresh flat-leaf parsley leaves, snipped with a scissors
2 tsp. fresh thyme

1. Preheat the oven to 425 degrees.

2. Prepare the sauce: In a large skillet, heat 2 tablespoons of the oil over high heat. When hot, reduce the heat to moderate and add the onions. Cook until soft and translucent, about 5 minutes. Season and set aside.

3. In another large skillet, heat the remaining 2 tablespoons oil over moderately high heat. When hot, add the garlic and cook until just tender and slightly brown, 2 minutes. Add the tomatoes and cook until the mixture thickens, about 10 minutes. Add the sugar and season.

4. Combine the onions and tomatoes, and continue cooking to thicken, about 10 minutes more. Taste for seasoning.

5. Meanwhile, prepare the potatoes: Peel, wash, and cut the potatoes into very thin slices. Wash again and dry thoroughly. In a small bowl, set aside about one quarter of the potatoes, which will be used as the topping. (For a particularly elegant presentation, trim the reserved potatoes into perfectly even rounds with a 1 1/2 inch pastry cutter.)

6. Rub the bottom of the baking dish with the garlic and 1 tablespoon of the butter.

7. In a large bowl, combine the remaining potatoes with the sauce, and with your hands, toss to blend. Transfer the mixture to the baking dish, smoothing it out with the back of the spoon. Add enough chicken stock to cover.

8. In a medium-size bowl, combine the reserved topping potatoes, the remaining 1 tablespoon butter, and the parsley. Toss to coat evenly. Beginning at one end of the dish, place the buttered potatoes, one by one, in slightly overlapping rows on top of the tomato-coated potatoes, until the entire dish is covered with an even potato layer. Sprinkle with the thyme.

9. Place the dish in the center of the oven and bake until the potatoes are soft, most of the liquid has been absorbed, and the top is golden, about 1 1/2 hours. Serve immediately.

Yield: 6 to 8 servings.