Peel and slice the potatoes as thinly as you can manage—if you have a mandolin, that would be perfect for the job. Make sure to immerse the potatoes in a bowl of water as you peel them, and slice them quickly, to avoid disclosing.

Just as soon as you're done peeling and slicing, pat the potato slices dry with paper towels. In a large mixing bowl, dress the slices with generous amounts of olive oil, salt and pepper, along with a few rosemary leaves and one or two cloves of garlic which you will have minced as finely as possible. (Here's one case when a garlic press comes in handy.) Set aside.

Take a large baking dish and rub the insides all over with the cut side of another clove of garlic which you will have sliced in half. Arrange the potato slices evenly in the dish, partially overlapping the top layer of potato slices like roof shingles, in a decorative pattern in the dish: lined up in rows if your dish is square or rectangular, in concentric rings if it's round or oval. Add enough water to come up about half the height of the potatoes—it's best to drizzle the water in at the sides of the dish so as not to displace the dressing. Drizzle the top of the potatoes with some more olive oil and sprinkle with some more salt. Finally, place a sprig of rosemary on top of the potatoes.

Roast the potatoes in a moderate (180C/350F) oven for about 45-60 minutes, until all the water has evaporated, the potato slices are soft inside and golden brown on top and around the edges. (Just how brown is a matter of taste—I like mine fairly lightly brown, as pictured.) If the potatoes are not brown enough for you, you can run them under the broiler for a minute or two, till they're done to your liking. Remove the rosemary sprig and let the dish rest for a good 1o minutes or so before serving directly from the baking dish.