Layered Mashed Potato & Mushroom Casserole

Layered Mashed Potato & Mushroom Casserole

11 Reviews
From: EatingWell Magazine, November/December 2009

Fancy up regular mashed potatoes with a layer of mushroom duxelle—a sauté of finely chopped mushrooms and shallots. We omitted the traditional butter in the duxelle and added chard for a nutritional boost. Serve this hearty side in place of mashed potatoes at any holiday feast or enjoy it as a vegetarian main dish.

Ingredients 12 servings

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Original recipe yields 12 servings
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  • 3½ pounds potatoes, preferably Yukon Gold, peeled and cut into 1-inch pieces
  • 1½ pounds cremini or white mushrooms, halved
  • 1 tablespoon butter
  • ½ cup nonfat buttermilk
  • 1 large egg plus 1 large egg white, beaten
  • 1¼ teaspoons salt, divided
  • 1 tablespoon extra-virgin olive oil
  • ¾ cup chopped shallots
  • 3 cloves garlic, finely chopped
  • 4 cups trimmed and finely chopped chard or spinach
  • 1 cup mushroom broth or reduced-sodium beef broth
  • 2 tablespoons all-purpose flour
  • ½ teaspoon freshly ground pepper
  • ½ teaspoon chopped fresh rosemary
  • 1 cup freshly grated Parmesan cheese, divided


  • Active

  • Ready In

  1. Bring 1 inch of water to a simmer in a large pot. Place potatoes in a steamer basket, cover and steam over medium-low heat, replenishing the water as necessary, until the potatoes are fall-apart tender, 20 to 30 minutes.
  2. Meanwhile, working in two batches, place mushrooms in a food processor and pulse, stopping to scrape down the sides as needed, until the mushrooms are coarsely chopped.
  3. Transfer the potatoes to a large bowl. Add butter and mash until chunky-smooth. Gradually stir in buttermilk, egg and egg white and 1 teaspoon salt. Set aside.
  4. Heat oil in a large skillet over medium heat. Add shallots and garlic and cook, stirring, until fragrant and beginning to soften, about 1 minute. Add the mushrooms and cook, stirring often, until they release their liquid and the pan is almost dry, 10 to 12 minutes. Add chard (or spinach) and continue to cook, stirring, until wilted, about 4 minutes. Whisk broth and flour in a small bowl. Add to the pan along with the remaining ¼ teaspoon salt, pepper and rosemary. Cook, stirring, until the mixture bubbles and thickens, about 1 minute.
  5. Preheat oven to 400°F.
  6. To assemble, spread half of the mashed potatoes in an even layer in a 9-by-13-inch (or similar 3-quart) baking dish. Sprinkle half the Parmesan over the potatoes. Spread the mushroom mixture on top and spread the remaining potatoes over the mushroom layer. Top with the remaining Parmesan.
  7. Bake until hot throughout and the top is golden brown, about 35 minutes.
  • Make Ahead Tip: Assemble through Step 6, cover and refrigerate for up to 1 day. Bake, uncovered, in a 400°F oven until hot, 50 minutes to 1 hour. To reheat, bake, covered, at 350° until hot, 40 to 50 minutes.
  • Keep food fresh: If you’re storing food in your fridge for a few hours or more, it’s best to keep it in an airtight container or in a container covered tightly with foil. Foil is best at creating a barrier that doesn’t let unwanted flavors in (or out) while you store your food.

Nutrition information

  • Serving size: about ¾ cup
  • Per serving: 192 calories; 5 g fat(2 g sat); 3 g fiber; 32 g carbohydrates; 7 g protein; 36 mcg folate; 24 mg cholesterol; 3 g sugars; 0 g added sugars; 910 IU vitamin A; 12 mg vitamin C; 92 mg calcium; 1 mg iron; 451 mg sodium; 776 mg potassium
  • Nutrition Bonus: Vitamin C (20% daily value)
  • Carbohydrate Servings: 2
  • Exchanges: 2 starch, 1 fat

Reviews 11

February 26, 2015
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By: EatingWell User
Use leftover mashed potatoes to simplify the dish If you have the time to follow the recipe precisely, you're in for a treat. But you won't be disappointed if you simply make mashed potatoes as normally do (leave out the egg), or use yesterday's mashed potatoes to make this. Skip the food processor and just slice or chop the mushrooms quickly (they'll break up when you saute them). Make layers as described and you're done! Pros: Great for using leftovers
December 26, 2011
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By: My Obsession
Used this to compliment the prime rib for Christmas dinner. It was absolutely fantastic. Highly recommend it as is and completely worth the effort!
September 23, 2011
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By: andrea
Tasty though time consuming Just made this last night as a main dish. Ended up taking me close to 3 hrs to make it - it took more time than I thought to prep the potatoes and chop all those mushrooms (in batches in the food processor). Also, I don't know how they "layer" mashed potatoes on top of the mushroom mix which is a lot softer. I ended up piping the potatoes through a plastic bag and just smearing them around. Next time I'll probably use prepped frozen potatoes and add more liquid so they spread easier. The end result was very good though! Pros: tastes great, not complicated Cons: time consuming
November 20, 2010
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By: EatingWell User
Made this last year for Thanksgiving and it's been requested for THIS year's holiday table. I'm going to add Swiss Chard to the spinach and a wider variety of mushrooms this year. With 2 vegetarians at the table, this will be a hit again, I'm certain.
November 09, 2010
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By: EatingWell User
November 09, 2010
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By: EatingWell User
Having my son's vegetarian girlfriend for Thanksgiving made me try a bit harder on side dishes and this one was truly a find! I expect I will always have it for holidays! The duxelle was fancy and so delicious. My son loves mushrooms and chard, and we all love good food so it was a hit with everyone. I made a portobello gravy from another garlic mashed potatoes recipe.and it was spectacular with it. Good with tofurkey and/or turkey!
May 20, 2010
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By: EatingWell User
this was delish the first nite and not so good every nite after - DRY! the mashed potatoes were like eating a baked potato not fully cooked! other than that, it was good and will probably make again (although a bit time consuming) - i'll just add milk or chicken broth to it so the leftovers aren't so dry!
March 21, 2010
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By: EatingWell User
I, too, made this for Thanksgiving dinner and will make it again at Easter. It was absolutely delicious. I used spinach, too, but will try blanched kale next time for a nutritional boost. If you love mashed potatoes, Gruyere cheese and mushrooms (and even if you HATE mushrooms, apparently, as one of our Thanksgiving diners told us---but he had 2nds and 3rds!), you cannot go wrong with this recipe.
December 03, 2009
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By: EatingWell User
This was a hit at Thanksgiving for my family! I used spinach because I had it on hand! I also must say it was fantastic as leftovers as well! Great recipe and pretty easy too!
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