This dish is 100% comfort food, and is a cross between potatoes au gratin and lasagna. With the potatoes are layers of mushrooms, onions, chard, and fresh basil. The cashew sauce makes the dish rich and creamy (see Notes for low-calorie options).
In my experience, this dish works best with russet potatoes, since they are starchier and soften nicely during cooking. I have used Yukon golds, too, but they a require longer cooking time, thus overcooking the other vegetables a bit. This dish has multiple steps and takes a bit of preparation, but the final result is worth it. I suggest reading the entire recipe through once first before starting. This makes excellent leftovers! You can reheat them in a microwave, or put a portion or two in a nonstick pan with a little water in the bottom and on the underside of the lid, and heat covered on medium-low until heated through.
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Mushroom-Basil Au Gratin
- Total Time: 1 hour 10 mins
- Yield: 6 to 8 1x
Ingredients
- For the casserole:
- 1¼ pounds russet potatoes (2 to 3 medium), peeled and thinly sliced (see step 2)
- 1 medium yellow or white onion, halved and thinly sliced (about 1½ cups)
- ½ pound medium white or cremini mushrooms, thinly sliced (about 1½ cups)
- 4 cups coarsely chopped Swiss chard or spinach
- 1½ cups chopped fresh basil (about 40 medium-large leaves)
- 1 ounce raw, unsalted cashews (about ¼ cup; for garnish)
- For the sauce:
- 2 cups unsweetened nondairy milk (I like soy milk)
- 2 ounces raw, unsalted cashews (about ½ cup)
- 1 tablespoon dried Italian herb seasoning
- 1 teaspoon granulated onion
- ½ teaspoon granulated garlic
Instructions
- To make the sauce, place all of the sauce ingredients (nondairy milk, cashews, Italian herbs, and granulated onion and garlic) into a blender, and set aside (so the cashew can soften).
- To slice the potatoes thinly and uniformly (like potato chips), I suggest using a mandolin slicer. If you do not have a mandolin, use a chef’s knife and aim for about a ⅛-inch thickness. Place the sliced potatoes, onions, mushrooms, and chopped chard/spinach and basil each into their own bowls.
- Preheat the oven to 375°F. Set aside a 13×9-inch baking dish (you do not need to oil or use parchment paper).
- Blend the sauce thoroughly until smooth. Next, we will prepare the casserole by creating layers as follows in steps 5 through 9:
- Pour a thin layer of sauce into the dish so it coats the bottom evenly.
- Layer one-third of the potatoes across the bottom of the pan, only slightly overlapping them. Use the thickest and biggest potatoes on the bottom.
- Next, add half of the onions, half of the mushrooms, half of the basil, and half of the chard/spinach. Pour about half of the remaining sauce over this.
- Next, add another layer, starting with a layer of potatoes (use the smaller and any odd looking potatoes for this layer), followed by the remaining onions, mushrooms, basil, and chard/spinach.
- Now, finish the casserole with a final layer of potatoes, creating a nice-looking “roof” to your casserole. Pour the remaining sauce evenly over the top.
- Cover the dish with a glass lid (if it has one) or aluminum foil (make sure the foil doesn’t touch the food, and seal the edges). Bake for 30 minutes.
- Remove the foil (careful of the hot steam). Using a rotary cheese grater to create a cheese-like topping, grate the ¼ cup cashews evenly across the top, and cook uncovered for 5 minutes more, or until the potatoes are tender when pierced with a knife and the edges are lightly browned. Let stand for 5 minutes before serving.
Notes
For a lower-calorie dish, in the sauce use 1 cup water and 1 cup nondairy milk, and/or decrease the amount of cashews from ½ cup to ¼ cup. You can also omit or reduce the grated cashews on top.
If you have a high-sided (deep-dish) 9x13 casserole dish, this would be a great use for it. The layers can get pretty high, but if using a regular 9x13 dish (not deep dish), just press down on the layers with your hands before placing the last layer of potatoes.
- Prep Time: 35 mins
- Cook Time: 35 mins
Nutrition
- Serving Size: ⅛ recipe
- Calories: 155
- Sugar: 2.9g
- Sodium: 52mg
- Fat: 6g
- Saturated Fat: 1g
- Carbohydrates: 21g
- Fiber: 3.1g
- Protein: 6.7g
- Cholesterol: 0
We made this for dinner tonight and served it alongside a broccoli slaw. So tasty! Thanks for sharing 🙂
Great! This is one of my favorites 🙂 Glad you enjoyed it.
This looks so yummy, but I'm having trouble finding the ingredients now, in March. might you have variation suggestions for the Winter/Spring season?
I've never had any trouble finding fresh basil. Even regular supermarkets normally have it all year around in those small plastic clamshell containers. And, if you can't find chard, you could substitute fresh spinach.
Hi Renee, you might try Whole Foods; they usually have basil, but it may cost a bit more. Otherwise, you can use another fresh herb (tarragon, parsley, cilantro) but I don't think it would have that same zip as the basil brings. Same with the chard; can be found at Whole Foods. Hope that helps 🙂
can you substitute another milk for sy
i have a soy allergy?
thanks
Sure, 🙂 Any kind will work as long as it's unsweetened.
This looks so yummy, Cathy- will make real soon! Thanks for such a great site!
Hi Joan! 🙂 Nice to see you!
This dish looks divine and I think my daughter's kids (both little, tiny vegans) would love it. Can't wait to make it. 🙂
Delish!! The third batch in as many days is now in the oven. It's so easy to make with my new Tribest blender and mandoline! I keep forgetting to get mushrooms, though. I've made it with yukon gold potatoes, sweet potatoes, and now with yams. Tomorrow I think I'll try a new recipe.:)
Hi Saffron! 😉 Glad it went over so well! Great to meet you at TN! -Cathy
I made this for my condo's potluck Holiday (Christmas) Party today, and it was very popular. Through long experience, I have learned not to label anything as "vegan ". Just put it out there and let people enjoy.
This was one of the first dishes used up even though most people here are fond of meat. Maybe a meat and potatoes thing, and I supplied the potatoes?
Anyway, thank you very much forthis recipe!
Hi Lynn, that's great! Thanks for the comment. 😉
This is one of my all time favorites - especially for company or groups. I think this recipe might be the nudge to get me to buy a madolin slicer! Thank you - YUMMM.
Hi Cathy,
I got back from TN about 2weeks ago, and I've made quite a number of dishes, but my husband told me tonight that this was his new favourite. So, thanks!
Nice! 🙂 Thanks Lindsay!
The broth didn't set for me; I think it needed flour or something to thicken it. Otherwise this was a great recipe thank you!
Can I use something instead of cashews here?
Any kind of nut or seed is fine; you just want some fat in there for richness.
Can I use white beans in place for the nuts in the sauce? I have a nut allergy.
I have wondered this and don't think beans would work very well; but if you try and it and it works, please let me know. 🙂
I tried it, turned out as a soup. Over blending the sauce probably didn't help though.
Do you think this casserole could be frozen successfully after it has been cooked?
I think so. 🙂
I don't have fresh basil on hand. Could I use dried?
Not for this recipe, since so much is used. You could really reduce the amount and just sprinkle on some dried basil, or other dried seasoning that you like. 🙂
I used 1/2 the amount of ground Italian seasoning and I used the whole bag of LITTLE potatoes at Aldi which I julianned. Did not layer, but mixed all together. It was yummy.
It makes a big batch. Does it freeze?
Not sure, but with the creamy sauce and potato slices, I don't think this is the best candidate for freezing.
I didn't think so either. Potatoes just don't....
I am not a fan of Italian seasoning. I even cut it in half. What can I
use instead?
You can use any spice or blend that you like really. 🙂