Melt butter in a small skillet over medium heat. Add garlic. Cook 2 minutes or just until garlic is lightly browned. Remove from heat, and stir in rosemary and thyme; set aside.
Brush bottom and sides of a 9" cast-iron skillet with 2 tablespoons oil. Arrange enough potato slices to cover bottom of skillet, overlapping slices; drizzle with one-third herbed garlic butter. Sprinkle with 1/4 teaspoon salt and 1/4 teaspoon pepper. Repeat procedure twice with remaining potato, herbed garlic butter, salt, and pepper. Brush a piece of aluminum foil with melted butter; press foil firmly, buttered side down, onto potato slices.
Bake at 400º for 1 hour and 10 minutes. Remove from oven, and using an oven mitt, press down firmly on the aluminum foil-covered potatoes. Remove aluminum foil, and place skillet on stovetop over medium heat. Cook 5 minutes. Remove from heat; let stand 2 minutes. Invert potatoes onto a plate, coaxing potatoes loose from skillet with a spatula.
Make Ahead: Bake potatoes Anna earlier in the day; invert onto an ovenproof plate, and cover loosely with foil. Just before serving, uncover and reheat at 400° for 10 minutes.