Position a rack in the upper third of the oven and preheat to 425 degrees F. Generously brush a large skillet with butter, then rub with the garlic. Heat the skillet over medium-high heat. Add half of the potatoes, sprinkle with 3/4 teaspoon salt, and pepper to taste, then arrange the remaining potatoes on top. Sprinkle with 3/4 teaspoon salt, and pepper to taste. Pour the broth and milk over the potatoes, then add the nutmeg and bay leaves; simmer 3 minutes.
Generously brush a shallow baking dish with butter and slide the potatoes into the dish; arrange with a fork, if desired. (If your skillet is ovenproof, you can skip this step and bake the potatoes right in the skillet.)
Dot the potatoes with the cut-up butter and sprinkle with the gruyere. Bake until golden, about 25 minutes. Let rest 5 minutes before serving. Discard the bay leaves.