Mushroom Potato Gratin
By: 
Cuisine: Vegetarian
Ingredient prep: 
Cook time: 
Total time: 
Makes: 4 entree servings
 
Adapted from Deborah Madison's The New Vegetarian Cooking for Everyone. Discard all your previous notions of potato gratin, and prepare for rich, earthy flavors that practically beg for a glass of your favorite red wine.
Ingredients
For the gratin
  • 1 oz. dried porcini mushrooms
  • 1 C bechamel sauce (recipe below) or heavy cream
  • 2½ T butter, divided
  • 1 clove garlic, minced
  • 1 clove garlic, halved crosswise
  • 1½ lbs. baby red potatoes, sliced just thicker than ⅛"
  • 10 oz. white button mushrooms, sliced thin
  • Kosher or sea salt
  • White pepper
  • ⅓ C finely grated white cheddar (optional)
  • Truffle salt, for serving (optional)
For the bechamel sauce
  • 1 C whole milk
  • 1 bay leaf
  • 1 clove garlic, smashed
  • 2 thin slices of yellow onion
  • 2 T butter
  • 1½ T flour
  • ¼ C heavy cream or additional milk
  • ¼ t freshly grated nutmeg (or 1 pinch dried ground)
  • Kosher or sea salt
  • White or black pepper
Make It
  1. In a small mixing bowl, cover dried mushrooms with 1¼ cups warm water. Place a serving bowl or plate over the mushrooms to keep submerged and soak at least 20 minutes, or until needed.
  2. If making bechamel, gradually heat milk in a small saucepan with bay leaf, garlic, and onion until just boiling. Turn off heat. Melt butter over medium in a 1 to 2 quart saucepan, then sprinkle in flour and stir constantly with a wooden spoon for a few minutes. The mixture should bubble but not stick to the pan or turn golden--adjust heat as needed. Over medium low, whisk constantly while pouring warm milk mixture into the roux (the flour and butter). Increase heat while stirring or whisking so sauce just bubbles. Cook until thickened, stirring constantly, about 10 minutes. Pass through a fine mesh strainer, then stir in ¼ cup cream or milk. Season with nutmeg, plus salt and pepper to taste.
  3. Preheat oven to 350 degrees (F).
  4. Swish (technical term) the dried mushrooms around in the bowl with your hands, then set a fine mesh strainer lined with a damp paper towel or coffee filter over a liquid measuring cup. Strain mushroom liquid into the cup, pressing out excess liquid from mushrooms gently with back of a spoon. Return bechamel or add cream to a medium saucepan. Over low heat, whisk in 1 cup of the mushroom soaking liquid. Turn off heat and set aside.
  5. Chop rehydrated mushrooms into ¼ to ½" pieces. Melt 2 tablespoons butter in a small skillet or saucepan over medium heat. Add chopped mushrooms and sautee about 3 minutes. Add minced garlic and cook another minute, then remove from heat and season with a little salt and pepper.
  6. Rub a 2 quart gratin or baking dish with the cut sides of halved garlic clove, then grease with remaining butter. Make a flat layer of half the sliced potatoes, seasoning with salt and pepper. Cover with a flat layer of all the sliced mushrooms, then the sauteed mushroom and garlic mixture. Cover with remaining sliced potatoes, sprinkling with more salt and pepper. Pour reserved mushroom cream evenly over the gratin.
  7. Bake gratin for an hour on middle rack. Sprinkle with cheddar, if using, and bake for another 30 minutes, until gratin is bubbling and potatoes are tender. You should be able to see some liquid, as it won't all have been absorbed by the potatoes. Cool slightly before serving.
Notes
I topped servings with truffle salt that I bought for the potato and celery root gratin. As expected, it was divine.

Assemble the gratin up to 12 hours ahead of time. The potatoes will soften slightly, which is fine. Baking time should be approximately the same. If possible, let gratin rest at room temperature for up to an hour before baking.

The dried mushrooms I linked to on Amazon are reasonably priced, but you can probably find them for a little less at the grocery store, at least on a per ounce basis. Feel free to try other varieties of dried mushrooms.
Recipe by Natural Comfort Kitchen at http://www.naturalcomfortkitchen.com/mushroom-potato-gratin/