Preheat oven to 450 degrees F. Spread salt in an even layer in a 2-quart rectangular baking dish. Arrange potatoes in dish, pressing lightly into salt. Remove the loose paper coating from garlic, keeping cloves intact. Cut the top 1/2 inch from the garlic bulb. Brush with some of the oil. Place garlic, cut side up, and herbs around potatoes. Cover baking dish with foil. Bake for 1 hour. Remove and discard herbs. Remove garlic and set aside to cool. Brush potatoes with remaining olive oil. Bake, uncovered, 15 minutes more or until tender.
Squeeze garlic from cloves into a small bowl. Add softened butter; stir to combine. Remove potatoes from salt and cut in half lengthwise; serve with garlic butter.