Prepare a grill using natural charcoal. When the coals are very hot, push them to one side of the grill to create a hot zone for direct grilling and a cooler zone for indirect grilling.
In a large bowl, toss the potatoes with the olive oil, and sprinkle with salt and pepper.
Place the potatoes on the cooler side of the grill, close the lid, and cook for about 1 hour, until the potatoes are tender when pierced with the tip of a knife.
Transfer the potatoes to a cutting board. Use the side of a large knife or the bottom of a heavy drinking glass to flatten each potato into a disk that is about 3/4-inch thick. The skins will split, but the potatoes should stay intact. Drizzle the creme fraiche over the potatoes, sprinkle with salt and pepper, and serve warm.
Adapted from "The Blackberry Farm Cookbook" by Sam Beall (c) Clarkson Potter 2009. Provided courtesy of Sam Beall. All rights reserved.