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Black Trumpet Mushroom and Yukon Gold Potato Gratin

Black Trumpet Mushroom and Yukon Gold Potato Gratin After a few days teaching in California, the chef at the Ritz in Paris asked Sarah to come to his Parisian kitchen and teach some healthy California cooking. While Sarah was in the Ritz kitchen, this chef taught her this very wicked thing. What evil French genius would teach a nice Georgia girl to simmer potatoes in porcini cream? I’d made black trumpet and potato gratin many a time, but I’d never realized it could be raised to such a level of fungal debauchery. Leaving the black trumpets in wide pieces adds a luscious silky texture to the gratin.

Serves 6

  1. Position a rack in the center of the oven, Preheat the oven to 350°F.
  2. Generously butter an 8-inch square baking dish.
  3. Place the cream, porcini mushrooms, and bay leaf in a medium heavy-bottomed saucepan. Bring to a boil, then turn off the heat and let steep for 20 minutes. Place a fine-mesh strainer over a medium bowl. Pour the cream mixture through the strainer, pressing on the porcini to extract all the cream. Discard the bay leaf. Return the cream to the saucepan. Whisk in 1 teaspoon of the salt and the pepper. Set aside. Thinly slice the porcini and set aside.
  4. Heat the oil in a large sauté pan over medium-high heat. When the oil is hot, add the black trumpet mushrooms, tossing quickly to coat with oil. Add the remaining ½ teaspoon salt. Cook, stirring occasionally, as the black trumpets release any liquid. Continue cooking and stirring until the liquid has evaporated. Add the garlic and cook for 1 more minute. Remove from the heat and cool. Stir in the porcini. Set aside.
  5. Peel the potatoes and place in a bowl of water to prevent browning.
  6. Bring the cream back to a simmer. Make sure the heat is low to prevent scorching. Remove the potatoes from the water and pat dry. Slice the potatoes very thin, ⅛-inch thick, on a mandolin or slicer. Add the potatoes to the simmering cream and cook for 5 minutes. The cream will become thick from the starch in the potatoes. Remove from the heat.
  7. Place one-third of the potatoes and cream in the prepared baking dish. Spread them out evenly over the bottom. Sprinkle with 1 tablespoon of the Gruyere. Top with half of the mushroom mixture, Make another layer using one-third of the potatoes and cream, 1 tablespoon of the Gruyere, and the remaining half of the mushrooms. Add the remaining one-third of the potatoes and top with the remaining 2 tablespoons of Gruyere.
  8. Place the baking dish on a baking sheet and cook for 30 minutes, or until the top is golden brown and the cream is bubbly. Remove the gratin from the oven and let sit for 10 minutes before serving.

Tips and Techniques

The baking sheet under the gratin prevents the potatoes from cooking too rapidly on the bottom before the top is done.

Substitutions and Variations

While the porcini mushrooms add a delicious flavor and richness to this dish, the gratin can be made without them. You can drizzle on some truffle oil just before serving to add a touch of elegance to the dish.