Sprinkle them with salt and the Herbes de Provence. Turn off the heat and set aside. Sprinkle with about a third of the Gruyere and Parmesan cheeses. Top with the onions, the nutmeg and another 1/3 of the cheeses. Layer the remaining sliced potatoes on top of the cheeses. Pour the half and half over everything. Sprinkle again with salt and pepper. Sprinkle the remaining one-third of the cheeses over everything. (At this point you can make a day ahead, just cover and refrigerate until time to cook.) Butternut Squash and Sweet Potato Gratin - from Pinch My Salt Truffled Chanterelle, Celery Root and Potato Gratin - from 101 Cookbooks
