Preheat oven to 350°.
Place 1/2-inch layer of rock salt in bottom of a shallow roasting pan. Arrange potatoes in a single layer on top of salt; pour remaining rock salt around and over potatoes. Bake at 350° for 50 minutes or until tender. Remove from oven; let stand 10 minutes. Rub excess salt from potatoes. Combine thyme, oil, and pepper in a bowl. Add potatoes; toss gently to coat.