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Casserole of Vegan Mushroom and Onion Scalloped Potatoes

Vegan Mushroom and Onion Scalloped Potatoes

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  • Author: Monkey and Me Kitchen Adventures
  • Prep Time: 30 Minutes
  • Cook Time: 35 Minutes (+Rest Time)
  • Total Time: 65 Minutes (+Rest Time)
  • Yield: 4 to 6 1x
  • Category: Dinner, Side
  • Method: Stovetop, Oven
  • Diet: Vegan


Rich, velvety, and bursting with the savory goodness of onions and mushrooms, this Vegan Mushroom and Onion Scalloped Potatoes is a true crowd-pleaser that will elevate any dinner or holiday spread.



Potato Boil Ingredients:

  • 24 oz. peeled and thinly sliced potatoes *
  • ½ to 1 teaspoon sea salt (+/-) * 

Skillet Ingredients:

  • 2 medium yellow onions, quartered, thinly sliced *
  • 1 Tablespoon minced garlic
  • 10 oz. Baby Bella mushrooms, thinly sliced *
  • 2 Tablespoons reduced sodium tamari *

Sauce Ingredients:

  • 1 cup [raw] cashews *
  • 1 cup low-sodium vegetable broth *
  • ¾ cup unsweetened plain plant milk
  • ¼ cup water
  • 1 Tablespoon distilled white vinegar
  • ¼ cup nutritional yeast
  • 1 teaspoon onion powder
  • 1 teaspoon garlic powder
  • ¼ teaspoon black pepper (+/-)
  • ¼ to 1 teaspoon sea salt (+/-) *
  • Pinch cayenne pepper *

Optional Ingredients:

  • 3 cups chopped fresh baby spinach *


  1. Preheat the oven to 425 F, center rack.
  2. Place the cashews into a small bowl, cover with boiling water and allow to sit for 15 minutes, then discard the water, and set aside until Step 6.
  3. Peel and thinly slice (about ¼ inch thickness) the potatoes, place into a stock pot, cover with cold water, add the sea salt, and bring to a boil, as soon as the water starts to boil, immediately reduce the heat to a gentle boil. Gently boil for 5 minutes, then immediately drain off the water, and gently rinse in cold water (to prevent further cooking and to set the starches in the potatoes) and set aside until Step 7.
  4. In a large skillet, add the finely sliced onions, sauté over medium-high heat for 7 to 9 minutes to soften, add a splash of water, if needed, to avoid burning. Then lower the heat to medium, add the minced garlic, sauté, stir constantly for one minute.
  5. Then add the sliced mushrooms and tamari to the skillet with the onions and garlic, stir well, then turn up the heat, sauté for 2 minutes, then lower the heat to a medium. Cover with a tight-fitting lid and allow the mushrooms to reduce in size, approximately 5 minutes. Once reduced, add the chopped baby spinach (if adding) and sauté just until wilted. Remove the onions, mushrooms, and spinach from the skillet, set aside.
  6. In the meantime, place the soaked cashews and all the remaining Sauce Ingredients into the high-speed blender, blend on high until smooth and emulsified, the add the sauce to the now empty skillet, cook until hot and bubbly, approximately 2 to 3 minutes, then remove from the stove.
  7. Place about ¾ cup of the sauce mixture on the bottom of a casserole dish. Divide the potatoes in half. Place layer half the potatoes in a single layer on the bottom of the casserole dish. Then put some of sauce over top of the potatoes. Then layer all the sauteed mushrooms, onions, spinach mixture, spread it out evenly. Place more of the sauce on top, then layer the other half of the par-boiled sliced potatoes in a single layer on top. Then pour all the remaining sauce over top of the par-boiled potatoes. Gently press down.
  8. Cover tightly with foil, then place into a preheated 425 F oven (center rack) and bake for 30 minutes. Remove the foil, test for potato tenderness by piercing the potatoes with a sharp knife. The knife should slide easily.
  9. Once the potatoes are tender (turn off the oven); however immediately place the back in the oven, uncovered for 5 minutes, then remove from the oven and allow to sit for 15 minutes to set up before serving.


*Please reference the blog post for Tips for Success, Pantry Items Used, Storage and Freezing, and Kitchen Products Used.

*Sea Salt:  Please adjust the sea salt based upon your family’s sea salt preferences and/or based upon dietary needs.

*Servings:  4 to 6