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Japanese Sweet Potato and Mushroom Gratin with Gruyère and Thyme

(recipe, Sophia Markoulakis)


Earthy mushrooms and chestnut-flavored potatoes make a rich side dish. Serve with a roasted chicken and a full-bodied Chardonnay.


  1. 12 oz. crimini mushrooms (about 6 cups sliced)
  2. 1 Tbsp. olive oil, plus more if necessary
  3. ¼ cup port wine
  4. 2 Tbsp. chopped fresh thyme
  5. ½ tsp. salt
  6. ¼ tsp. freshly ground pepper
  7. 2 lb. Japanese sweet potatoes
  8. 1 cup half-and-half
  9. 2 cups whole milk
  10. ¾ cup grated Gruyère cheese
  11. Salt and freshly ground pepper to taste


  1. Preheat oven to 350 degrees.
  2. Brush off mushrooms, trim their stems, and thinly slice. If large, slice in half first.
  3. Heat oil in a large nonstick skillet and sauté mushrooms on high, stirring often, until mushrooms are tender, about 8 minutes. Add port and continue to stir, scraping up any brown bits from bottom of pan, until all liquid evaporates. Remove from heat and add thyme and ¼ tsp. each of salt and pepper; stir to blend.
  4. Peel and thinly slice sweet potatoes (thickness should be about a sixteenth of an inch) and place in a large sauté pan filled with half-and-half and milk. Add remaining ¼ tsp. salt and slowly simmer over medium heat until mixture comes to a boil. Reduce heat and simmer for 10 minutes, stirring often, until potatoes are just tender.
  5. Strain half of the potatoes and place in a buttered 3-quart ovenproof baking dish so that they cover bottom of dish. Scatter mushrooms on top and add half of the cheese. Place remaining strained potatoes on top, covering the mushroom-cheese layer, and evenly pour milk mixture over potatoes. Sprinkle top with remaining cheese and season with salt and pepper to taste.
  6. Bake, loosely covered with foil, for 30 minutes. Remove foil and continue to bake for another 15 minutes, or until liquid bubbles and cheese lightly browns. Remove from oven and allow to sit for 15 minutes before serving.


Read more about sweet potatoes in Sophia Markoulakis' "Sweet potatoes."