Preheat oven to 450°F.

Peel the potatoes, and slice them very thin, barely thicker than chips. Wash them in cold water, then pat them thoroughly dry with cloth kitchen towels.

Put all the potatoes into a 10 x 16 baking dish, half the olive oil, half the garlic, half the parsley, several liberal pinches of salt, and black pepper. Toss the potatoes 2 or 3 times to coat them well, then spread them evenly over the bottom of the dish.

When the oven reaches the preset temperature, put the potatoes in the uppermost third of it and roast them for 12 to 15 minutes, until they are about halfway done.

Take out the dish, but do not turn off the oven. Put the fish fillets skin side down over the potatoes. Mix the remaining olive oil, garlic, and parsley in a small bowl, and pour the mixture over the fish, distributing it evenly. Sprinkle with liberal pinches of salt and black pepper. Return the dish to the oven.

After 10 minutes, take the dish out, but do not turn off the oven. Use a spoon to scoop up some of the oil at the bottom of the dish, and baste the fish with it. Loosen those potatoes that have become browned and are stuck to the sides of the dish, moving them away. Push into their place slices that are not so brown.

Return the dish to the oven and bake for 5 to 8 more minutes, depending on the thickness of the fish fillets.

Remove the dish from the oven and allow to settle a few minutes.

Serve directly from the baking dish, scraping loose all the potatoes stuck to the sides - they are the most delectable bits - and pouring the cooking juices over each portion of fish and potatoes.