Sweet Potato Gratin

1. Preheat oven to 400 F and use the softened butter to generously grease a baking dish that measures 8 x 8 x 2 inches (or a baking dish that will hold the equivalent volume).
2. Into a medium sized saucepan add the heavy cream, half-and-half cream, garlic and salt. Bring the liquid up to a boil over medium heat and then decrease the heat to medium-low and allow it to simmer for another 20 minutes. Remove the pan from the heat and remove and discard the garlic cloves. Set aside.
3. Remove 10 or 15 of the most attractive slices of sweet potatoes and keep those to the side, these will be used on the top layer. Use any broken or small slices of sweet potato in the middle layers.
4. Now to assemble the gratin. Spoon about ¼ cup of the cream into the bottom of the prepared baking dish. Place a layer of sweet potatoes, slightly overlapping them in the bottom of the dish. Ladle about ¼ cup of the cream over the sweet potatoes, sprinkle about 1/4 each of the sage and thyme over that and then top with a pinch of salt and pepper, and finally 1 tablespoon of the Parmesan cheese. Continue this sequence of layers until you run out of potatoes (don’t forget to use the reserved pretty slices for the top layer). When you get to the last layer pour all of the remaining cream over the top, but don’t sprinkle any cheese on the top layer yet. Reserve the remaining cheese.
5. Place the baking dish on a sheet pan, lay a sheet of aluminum foil loosely over the top, and bake covered for about 20 minutes. Then remove the foil and bake for another 20 minutes. And finally, sprinkle the remaining cheese over the top of the potatoes and bake for 15 minutes longer. The gratin is done when a paring knife will go easily into the center. Remove from the oven and allow the gratin to sit for about 10 minutes before cutting and serving.

Note: This recipe is easily doubled. In that case a 13 x 9 x 2 should be fine. There will just be a couple more layers, but it will easily fit. Increase the time that the gratin is baked covered to 35 minutes.