1. Heat oven to 425 degrees. Wrap garlic in foil, or place in garlic roaster, and roast until garlic is turning golden and head is soft, about 1 hour. Let stand until cool enough to handle. Slice off tip of head, just enough to expose cloves; press out garlic, using back of knife to help. Discard garlic skin; transfer garlic to small bowl. Add 1 1/2 tablespoons oil, 1 teaspoon salt, and 1/4 teaspoon pepper. Smash together with back of teaspoon to create thick paste.

2. Raise oven to 475 degrees. Slice each potato into three or four one-inch-thick pieces. Spread a generous amount of paste between each slice; reassemble potato, pressing on chunks so potato sticks together. Set potato on a piece of foil, drizzle with 2 teaspoons oil, and salt and pepper to taste. Wrap potato tightly in foil; repeat process with other potatoes. Bake potatoes on baking sheet until they are soft and have a caramelized roasted-garlic crust on the bottom, about 1 hour and 10 minutes. Serve on bed of fresh thyme.