Sweet Potato & Mushroom Gratin

Tomorrow I'm teaching a joint holiday cooking class with my good friend Nancy. The class features some of our favorite Thanksgiving recipes. Nancy will be teaching a roasted cranberry chutney, a delicious raw kale and apple salad and her amazing pecan pie. My contribution will be my grandmother's dinner rolls, pumpkin pot de crème and a simple gratin of sweet potatoes and mushrooms. Today, I thought I would give a sneak peak at the sweet potato recipe.


In my house it wasn't Thanksgiving without sweet potatoes on the table. Even so, there wasn't one ultimate version that continued to show up year after year. With all of the other things that had to be on the table for the sake of tradition, sweet potatoes were the one thing my mother experimented with. I remember many tasty versions: one with carrots...another with pineapple...several sugar-y glazed versions.... Fortunately, my mother would never have dreamed of putting marshmallows on the table, so I have no memory of ever being subjected to that ghastly concoction.

Over the years I have served all kinds of delicious sweet potato dishes on the Thanksgiving tables of my adulthood—maple whipped... in a gratin with apple and dried fruit... a purée with roasted apples...etc. All are delicious (I love sweet potatoes). Unfortunately, none of these were candidates for inclusion in tomorrow's class because I have taught them all before in other classes—classes that are still in my current rotation. Not wanting to let a "favorites" class go by without sweet potatoes, I decided to come up with something new.

As I began to consider what to make, I immediately thought of mushrooms. Mushrooms are fabulous with some of the sweeter vegetables—corn...winter squash...and sweet potatoes. Mushrooms are also a nice savory change from the sweet types of things that are typically paired with sweet potatoes at the holidays.

I thought about making a classic layered gratin of thinly sliced sweet potatoes with a middle layer of sautéed mushrooms (similar in style to the sweet potato-turnip gratin I posted a couple of years ago), but discarded the idea for a couple of reasons. The first is that I teach these types of gratins a lot (they are delicious). The second has to do with the fact that they take a long time in the oven at a fairly low temperature. This makes them difficult to manage on Thanksgiving day. They can be made ahead and reheated, but they are at their absolute best when freshly made.

Then I remembered the unusual gratin of artichokes and mushrooms that I posted last Spring. The idea of this gratin—a shallow casserole with a layer of fully cooked chunky vegetables, drizzled with a touch of cream and topped with cheese and buttery breadcrumbs—seemed like a perfect style of dish for the Thanksgiving table. Every one of the components can be made ahead and the final dish takes less than half an hour in the oven. Sounds to me like a perfect recipe for a new Thanksgiving favorite.

The gratin made a delicious weeknight meal with a kale, apple and sausage salad.

Gratin of Sweet Potatoes & Mushrooms

1 1/2 T. unsalted butter
1 lb. Garnet or Jewel Sweet Potatoes, peeled and cut into 1/2- to 3/4-inch pieces
5 to 6 oz. (about 5 large) shallots, trimmed, peeled and sliced (lengthwise) 1/4-inch thick
1 T. picked fresh thyme leaves
1/3 c. chicken stock or water
Salt & pepper

1 T. Olive oil
1/2 T. unsalted butter
8 oz. crimini mushrooms, halved or quartered, depending on their size
Chicken Stock, water or dry Sherry

1/2 c. heavy cream
1 to 1 1/2 T. dry Sherry
2 to 2 1/2 oz. coarsely grated Gruyère cheese
1 c. coarsely ground fresh breadcrumbs
1 to 2 t. unsalted butter

Butter an 8- by 8-inch square (or equivalent sized) shallow gratin, casserole or baking dish. Set aside.

Melt 1 1/2 T. of butter in a medium-sized sauté pan (a pan just large enough to hold the sweet potatoes in a snug single layer) set over moderate heat. Add the sweet potatoes and shallots and toss to coat in the fat. Allow the vegetables to sizzle in the butter (increase the heat if they aren't sizzling), stirring now and then, until the shallots have begun to soften and the sweet potatoes are golden in a few spots—about five minutes.

Deglaze with the chicken stock—gently scraping with a flat wooden spoon or heat proof spatula—to release the caramelize bits from the bottom of the pan. Add the thyme and season well with salt & pepper. Reduce the heat to very low, cover and cook until the sweet potatoes are tender but not falling apart—about 15 to 20 minutes.

Stir the sweet potatoes once or twice as they cook. If the liquid evaporates too rapidly, add a bit more stock or water. When they are done, there should be a tablespoon or so of syrupy liquid in the bottom of the pan. If there is more than this, remove the lid from the pan and continue to cook until the excess liquid evaporates. Transfer the contents of the pan to the prepared baking dish.

While the sweet potatoes cook, sauté the mushrooms: In a medium sauté pan, heat the olive oil and butter over medium heat. When the butter is melted, increase the heat to medium-high. When the foam subsides, add the mushrooms and sauté until golden brown in spots and tender. Wait to add salt until the mushrooms have begun to brown. Deglaze the pan with a splash of stock, water or sherry. Reduce the liquid to a glaze. Scatter the mushrooms over the sweet potatoes, encouraging them to nestle down in among the sweet potatoes.

The gratin may be made to this point ahead. Let the vegetables cool, then cover and refrigerate. Bring the dish to room temperature before proceeding with the recipe.

Build the gratin: Combine the heavy cream and sherry. Drizzle over the vegetables. The liquid will only be about a quarter of an inch deep in the dish.  Scatter the cheese evenly over the surface of the vegetables followed by the breadcrumbs. Dot with butter. (Or, if you prefer, melt the butter and toss the breadcrumbs with the melted butter before spreading them over the cheese covered vegetables.)

Place the gratin in the upper third of a hot oven (400° to 425°) and bake until the crumbs are beginning to turn golden, the cream is bubbling and reduced around the edges and the gratin is hot in the center—about 20 minutes. If, when the gratin is hot through, the crumbs are not as brown as you would like, briefly run under the broiler.


Serves 6 as part of a Thanksgiving spread.

Notes:
• Recipe is easily doubled to fit a 13- by 9-inch (or equivalent sized) baking dish.
• For tips on how to prepare this type of gratin, check out the post for the artichoke gratin. The most important thing is to choose a proper style and size of baking dish. You can make this gratin any size you like as long as you choose a shallow dish and spread the cooked vegetables in a snug, single layer in that dish. Then simply drizzle in cream to a depth of about 1/4 to 1/3 of an inch.

If the vegetables are piled too deeply in the dish, you won't have a proper ratio of cream to vegetables. Moreover, the vegetables in the center will not be hot by the time the cream has begun to bubble and reduce. If allowed to reduce too long, the butter will break out of the cream and the dish will be oily instead of creamy.

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