Layered Mashed Potato and Mushroom Casserole

The aroma always hits me first – earthy mushrooms mingling with the comforting scent of mashed potatoes. It takes me back to my grandmother’s kitchen, where she would prepare this casserole every Thanksgiving. The entire family would gather, drawn in by the promise of savory goodness. Her version always had a secret ingredient: a pinch of nutmeg in the mashed potatoes. This recipe, while slightly different, evokes the same warm feelings of home and family.

Recipe Overview

• Prep Time: 30 minutes
• Cook Time: 35 minutes
• Total Time: 1 hour 5 minutes
• Servings: 12
• Yield: One 9×13-inch casserole
• Dietary Type: Vegetarian

Ingredients

• 3 1/2 lbs Yukon gold potatoes, peeled and cut into 1-inch pieces
• 1 1/2 lbs cremini mushrooms, halved
• 1 tablespoon butter
• 1/2 cup fat-free buttermilk
• 1 large egg plus 1 large egg white, beaten
• 1 1/4 teaspoons salt, divided
• 1 tablespoon extra virgin olive oil
• 3/4 cup chopped shallot
• 3 garlic cloves, finely chopped
• 4 cups trimmed and finely chopped chard leaves (may sub spinach)
• 1 cup mushroom broth (may sub any veggie broth)
• 2 tablespoons all-purpose flour
• 1/2 teaspoon fresh ground pepper
• 1/2 teaspoon chopped fresh rosemary
• 1 cup freshly grated Parmesan cheese, divided

Equipment Needed

• Large pot with steamer basket
• Food processor
• Large bowl
• Large skillet
• Small bowl
• 9-by-13-inch baking dish (or similar 3-quart)

Instructions

1. Begin by preparing the potatoes. Bring about an inch of water to a simmer in a large pot. Place the potatoes in a steamer basket, cover, and steam over medium-low heat. Ensure you replenish the water as needed to prevent the pot from drying out. Steam the potatoes until they are easily pierced with a fork and fall apart tender, approximately 20 to 30 minutes. The exact time will depend on the size of your potato pieces and the heat of your stove.

2. While the potatoes are steaming, prepare the mushrooms. Working in two batches, place the cremini mushrooms in a food processor. Pulse, stopping to scrape down the sides of the bowl as needed, until the mushrooms are coarsely chopped. Don’t over-process, as you don’t want a mushroom paste. You want to retain some texture.

3. Once the potatoes are steamed, transfer them to a large bowl. Add the butter and mash until the potatoes are chunky-smooth. Gradually stir in the fat-free buttermilk, the beaten egg, and the beaten egg white, followed by 1 teaspoon of the salt. Set the mashed potatoes aside.

4. Now, focus on the mushroom duxelles. Heat the extra virgin olive oil in a large skillet over medium heat. Add the chopped shallots and finely chopped garlic. Cook, stirring frequently, until they become fragrant and begin to soften, about 1 minute. Be careful not to burn the garlic as it can turn bitter very quickly.

5. Add the coarsely chopped mushrooms to the skillet. Cook, stirring often, until the mushrooms release their liquid and the pan is almost dry, about 10 to 12 minutes. The mushrooms will significantly reduce in volume as they cook and release moisture.

6. Add the finely chopped chard leaves (or spinach) to the skillet with the mushrooms. Continue to cook, stirring, until the chard (or spinach) is wilted, approximately 4 minutes.

7. In a small bowl, whisk together the mushroom broth and all-purpose flour until smooth. This slurry will help to thicken the mushroom mixture. Add the broth mixture to the skillet along with the remaining 1/4 teaspoon of salt, the fresh ground pepper, and the chopped fresh rosemary. Cook, stirring constantly, until the mixture bubbles and thickens, about 1 minute.

8. Preheat your oven to 400°F (200°C).

9. To assemble the casserole, spread half of the mashed potatoes in an even layer in the bottom of a 9-by-13-inch (or similar 3-quart) baking dish. Sprinkle half of the freshly grated Parmesan cheese evenly over the potatoes.

10. Spread the cooked mushroom mixture evenly over the potato and Parmesan layer.

11. Spread the remaining mashed potatoes over the mushroom layer, creating a smooth top.

12. Top the casserole with the remaining freshly grated Parmesan cheese.

13. Bake in the preheated oven until the casserole is hot throughout and the top is golden brown, about 35 minutes. To ensure even baking, rotate the casserole halfway through the baking time.

14. Remove from the oven and let cool slightly before serving.

15. MAKE AHEAD INSTRUCTIONS: Assemble the casserole through Step 6, cover tightly with plastic wrap or foil, and refrigerate for up to 1 day. Bake, uncovered, in a 400°F (200°C) oven until heated through, about 50 minutes to 1 hour. If the top begins to brown too quickly, cover loosely with foil. To reheat a previously baked casserole, bake, covered, at 350°F (175°C) until heated through, about 40 to 50 minutes.

Expert Tips & Tricks

• For extra creamy mashed potatoes, consider using a potato ricer instead of a masher.
• If you don’t have mushroom broth, chicken broth or vegetable bouillon works just as well.
• Adjust the amount of Parmesan cheese according to your taste. A sharp cheddar or Gruyere would also be delicious.
• For a richer flavor, sauté the mushrooms in a combination of butter and olive oil.
• Be careful not to overcook the mushrooms, as they can become rubbery.

Serving & Storage Suggestions

Serve the Layered Mashed Potato and Mushroom Casserole hot as a side dish with roasted chicken, beef, or pork. It also makes a wonderful vegetarian main course. Garnish with a sprig of fresh rosemary or a sprinkle of chopped parsley for a beautiful presentation.

Leftovers can be stored in an airtight container in the refrigerator for up to 3 days. To reheat, bake in a preheated oven at 350°F (175°C) until heated through. You can also reheat individual portions in the microwave. For longer storage, the casserole can be frozen for up to 2 months. Thaw completely in the refrigerator before reheating.

Nutritional Information

Nutrient	Amount per Serving	% Daily Value
Calories	198.9 kcal	N/A
Calories from Fat	42 g	21%
Total Fat	4.7 g	7%
Saturated Fat	2.3 g	11%
Cholesterol	9.9 mg	3%
Sodium	416.7 mg	17%
Total Carbohydrate	32.8 g	10%
Dietary Fiber	3 g	11%
Sugars	2.4 g	N/A
Protein	8.1 g	16%

Note: Nutritional information is an estimate and may vary based on specific ingredients and preparation methods.

Variations & Substitutions

• Vegan Option: Substitute the butter with a vegan butter alternative, use plant-based milk instead of buttermilk, and omit the egg and Parmesan cheese or substitute with nutritional yeast.
• Gluten-Free: Ensure the broth is gluten-free. You may also use a gluten-free all-purpose flour blend or cornstarch in place of the all-purpose flour.
• Vegetable Variations: Add other vegetables to the mushroom mixture, such as diced carrots, celery, or bell peppers.
• Herb Variations: Experiment with different herbs such as thyme, sage, or oregano instead of rosemary.
• Cheese Variations: Try using different cheeses such as Gruyere, fontina, or mozzarella in place of the Parmesan cheese.

FAQs (Frequently Asked Questions)

Q: Can I use a different type of potato?
A: While Yukon gold potatoes provide a creamy texture, you can use other types of potatoes such as Russet potatoes or red potatoes. Keep in mind that Russet potatoes will result in a drier mash, so you may need to add more buttermilk or butter to achieve the desired consistency.

Q: Can I make this casserole ahead of time?
A: Yes, this casserole can be assembled ahead of time and refrigerated for up to 24 hours before baking. This makes it a great option for holiday gatherings or potlucks.

Q: Can I freeze this casserole?
A: Yes, this casserole freezes well. Wrap it tightly in plastic wrap and then in foil before freezing. Thaw completely in the refrigerator before baking.

Q: What can I use if I don’t have chard?
A: Spinach makes an excellent substitute for chard. You can also use kale, but you may need to cook it slightly longer to soften it.

Q: Can I add meat to this casserole?
A: Yes, you can add cooked and crumbled sausage, bacon, or ground beef to the mushroom mixture for a heartier casserole.

Final Thoughts

This Layered Mashed Potato and Mushroom Casserole is more than just a recipe; it’s a celebration of flavors and a tribute to home cooking. The combination of creamy mashed potatoes, savory mushrooms, and fragrant herbs creates a truly unforgettable dish. I encourage you to try this recipe and make it your own by adding your personal touch. Feel free to share your feedback and any variations you come up with. Serve it alongside your favorite holiday meal or enjoy it as a comforting vegetarian main course. I promise you, it will be a hit!