How to Make It
Preheat the oven to 350°. In a bowl, mix 4 cups of kosher salt with 1/2 cup of water. Spread half of the salt in a 9-by-9-inch baking dish. Arrange the potatoes in the baking dish and pack the remaining salt on top.
Bake the potatoes for 45 minutes, until tender. Let cool. Crack the salt crust and carefully remove it. Transfer the potatoes to a work surface and cut them into 1-inch pieces.
Lower the oven to 200°. Light a grill. Brush the steak with oil and season with salt and pepper. Rub the steak with the garlic and 2 teaspoons each of the sage, rosemary and thyme.
Grill the steak, turning, until charred. Transfer to a rimmed baking sheet and bake until an instant-read thermometer registers 125° for medium-rare. Transfer to a board and let rest for 15 minutes.
In a skillet, heat 1/4 cup of oil. Cook the potatoes over moderately high heat, tossing, until browned. Add the bread crumbs and remaining 1 teaspoon each of the herbs and cook, tossing, until the bread crumbs are toasted, 4 minutes. Season with kosher salt and pepper. Slice the steak; spoon any juices on top and sprinkle with Maldon salt. Serve.