Scrub potatoes; set aside. Pour salt into the bottom of a 12-inch heavy cast-iron skillet or Dutch oven, spreading evenly. Heat over medium heat about 5 minutes or until hot. Sprinkle evenly with fennel seeds.
Add potatoes to hot salt in skillet, pressing potatoes into salt slightly. Cover skillet. Cook 35 to 40 minutes or until tender when tested with a fork. Remove skillet from heat. Let stand, covered, for 5 minutes.
Remove potatoes from skillet with tongs and brush excess salt from potatoes (reserve salt mixture). Transfer potatoes to a serving platter. Drizzle with olive oil. Cover with foil and let stand 5 minutes. Serve with reserved salt mixture. Makes 4 to 6 servings.