Wash the potatoes to remove the dirt, but try not to remove the skins. Up to, say, golf-ball size, they can be roasted whole, but any larger than that and they should be cut into halves or quarters. Parboil the potatoes in a pan of salted water for 5 minutes, then drain and let dry for a minute or two.
Cut the 2 lemons into thick slices. Put the potatoes in a baking dish and scatter over the lemon slices, garlic, rosemary and thyme. Drizzle oil generously over everything and toss the whole lot together with your hands, making sure each potato is covered in oil. Season well with salt and pepper. Bake for 35 to 40 minutes, turning everything at least once, until the lemons are starting to caramelize and the potatoes look irresistibly golden brown.
Squeeze on the juice from the extra lemon half, sprinkle with a little more salt, and serve immediately.
Reprinted with permission from River Cottage Every Day by Hugh Fearnley-Whittingstall, copyright (C) 2009. Published by Ten Speed Press, a division of Random House, Inc.