This deliciously cheesy mushroom casserole features onions, thyme, and melted gruyere. Made without breadcrumbs and ready in about 40 minutes, it's low-carb and gluten-free.
This mushroom casserole is amazing. It's so cheesy and flavorful! The wonderful aroma it releases when you cook it will be your first hint that it's going to be sooo good. Mushrooms are one of my favorite vegetables (well, technically, they're fungi), and this delicious casserole is one of my favorite ways to cook them (these roasted mushrooms are amazing, too).
Ingredients
See the recipe card for exact measurements. Here are my comments on some of the ingredients.
- Olive oil: You can substitute it with butter or ghee.
- Baby Bella mushrooms: You can also use white mushrooms.
- Salt and pepper: I use kosher salt and freshly ground black pepper.
- Aromatics: Onions and garlic. While jarred minced garlic is convenient, freshly minced tastes significantly better.
- Spices: I use dried thyme and parsley.
- Shredded Gruyere cheese: Gruyere tastes best, but I've made this casserole with shredded sharp cheddar, Gouda, and provolone.
Instructions
The detailed instructions and step-by-step photos are included in the recipe card. Here's a quick overview.
Since mushrooms release quite a bit of liquid when cooked, you can't just put them in a dish and bake them. You need to saute them first. So, to make this recipe, I saute the mushrooms and chopped onions in olive oil until the mushrooms have released their liquid and most of the liquid has evaporated.
Once the liquid has mostly evaporated, you can transfer the mushrooms and onions to a greased baking dish and top them with cheese.
The last step is baking the casserole until the cheese has melted.
Our love of mushrooms knows no bounds, so when we saw this recipe, we knew we had to try it at our pre-Christmas gathering and it was a hit! I didn't change a thing, assembled it early in the day and because oven space was at a premium, simply nuked it to melt the cheese and reheat the mushrooms; as a make-ahead dish...full marks! Thank you for publishing this yummy recipe!
Lynn
Read more comments
Our love of mushrooms knows no bounds, so when we saw this recipe, we knew we had to try it at our pre-Christmas gathering and it was a hit! I didn't change a thing, assembled it early in the day and because oven space was at a premium, simply nuked it to melt the cheese and reheat the mushrooms; as a make-ahead dish...full marks! Thank you for publishing this yummy recipe!Recipe Tips
- If your casserole dish is broiler-safe, instead of baking, you can simply broil the casserole for 2-3 minutes in the middle of the oven until the cheese is melted. You don't want to get too close to the heating element and risk burning the casserole.
- I use a lot of mushrooms - 32 ounces. But keep in mind that mushrooms lose significant volume after they are cooked. Once cooked, they fit nicely in a 2-quart casserole dish.
- I like to use brown mushrooms because they make the casserole look more presentable than white mushrooms. So, I typically use baby Bella or crimini mushrooms.
- Since I'm lazy, I buy pre-sliced mushrooms and pre-chopped onions. Which makes this casserole super easy!
- Storage: Once the leftovers are cool, transfer them with a slotted spoon to an airtight container and keep them in the fridge for up to 4 days. Reheat them in the microwave at 50% power.
Serving Suggestions
- Mushrooms go well with steak, so I often make this recipe when I serve reverse-seared steak, New York Strip, or London broil.
- They are also perfect with chicken. Sometimes, I slice baked chicken breast and top the slices with this casserole.
- You can also serve this mushroom casserole as a main course, adding a simple side such as steamed broccoli, steamed asparagus, or tomato salad.
- It's the perfect holiday side dish that everyone will love! When I serve it for a holiday, I often pair it with ribeye roast, beef tenderloin roast, pork roast, leg of lamb, or roasted boneless turkey breast.
Recipe Card
Cheesy Mushroom Casserole
Video
Ingredients
- ¼ cup olive oil - plus more for the pan
- 32 ounces baby Bella or crimini mushrooms - sliced
- 2 teaspoons Diamond Crystal kosher salt - or 1 teaspoon of any other salt, including Morton kosher salt
- 1 cup onions - chopped
- 1 tablespoon fresh garlic - minced
- ½ teaspoon black pepper
- ½ teaspoon dried thyme
- 1 cup Gruyere cheese - shredded
- 1 teaspoon dried parsley - for garnish
Instructions
- Preheat the oven to 400°F. Grease a 2-quart baking dish with olive oil.
- Heat the olive oil in a large, deep skillet over medium-high heat. Add the mushrooms, onions, and kosher salt. Cook, stirring occasionally, until the mushrooms have released their liquid and the liquids have mostly evaporated, about 10 minutes.
- Add the garlic, black pepper, and thyme. Cook, stirring, for one more minute. Remove from heat.
- Transfer the mixture to the prepared baking dish. Sprinkle it with the shredded cheese.
- Bake the casserole until hot and bubbly, about 15 minutes. Sprinkle with parsley and serve.
Notes
- If your casserole dish is broiler-safe, instead of baking, you can simply broil the casserole for 2-3 minutes in the middle of the oven until the cheese is melted. You don't want to get too close to the heating element and risk burning the casserole.
- A good way to vary this recipe is to use different cheeses, such as cheddar, Gouda, or provolone.
- I use a lot of mushrooms - 32 ounces. But keep in mind that mushrooms lose significant volume after they are cooked. Once cooked, they fit nicely in a 2-quart casserole dish.
- I like to use brown mushrooms because they make the casserole look more presentable than white mushrooms. So, I typically use baby Bella or crimini mushrooms.
- Once the leftovers are cool, transfer them with a slotted spoon to an airtight container and keep them in the fridge for up to 4 days. Reheat them in the microwave at 50% power.
Nutrition per Serving
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Most recipes are low-carb and gluten-free, but some are not. Recommended and linked products are not guaranteed to be gluten-free. Nutrition info is approximate. Please verify it independently. The carb count excludes non-nutritive sweeteners. Please read these Terms of Use before using any of my recipes.
Donna D. Wolfe says
I made this for Thanksgiving dinner. It was a very tasty with turkey. I will definitely be making this again. Thank you for sharing.
Vered DeLeeuw says
You're very welcome, Donna! 🙂
Becky says
Followed recipe exactly. Was amazing! So flavorful! Making again this evening! Yum!
Vered DeLeeuw says
Yay! I'm so glad you liked this recipe, Becky! Thank you for the comment.
Susan says
I've read that cooked mushrooms can be frozen. Have you tried to freeze the mixture minus the cheese?
Vered DeLeeuw says
Hi Susan,
I haven't, but I believe it should work.
Dianna says
I made this recipe last night for dinner, using Shitake mushrooms and mozzarella cheese. Oh my goodness! They were so good and my hubby loved them! We grow our own Shitake mushrooms, which is why I used those.
Vered DeLeeuw says
I'm so glad you enjoyed this casserole, Dianna! I love shiitake mushrooms. How lucky you are to be growing them!
Sara says
It was so good that my 80 yr old Dad asked for the leftovers and recipe!
Vered DeLeeuw says
Yay! I'm so glad this was a success, Sara! Thanks for the review.
Lindsay says
I made this for Thanksgiving and it turn out just perfect!
Vered DeLeeuw says
Wonderful, Lindsay! I'm so glad you enjoyed this casserole.
Lynn says
Who would have thought to combine cheese with mushrooms?!! But this works! We all enjoyed this as one of our sides for dinner guests; it was such a nice addition to other vegetables, in a non-competitive way. I used sliced portobello mushrooms which also gave a lovely flavour. Thank you..who would have thought?! 🙂
Vered DeLeeuw says
I'm so glad you liked this recipe, Lynn! I love the idea of using portobello mushrooms.
Leslie says
Oh, Sooo Good!!
Vered DeLeeuw says
Glad you liked it, Leslie!
Lynn says
Our love of mushrooms knows no bounds, so when we saw this recipe, we knew we had to try it at our pre-Christmas gathering and it was a hit! I didn't change a thing, assembled it early in the day and because oven space was at a premium, simply nuked it to melt the cheese and reheat the mushrooms; as a make-ahead dish...full marks! Thank you for publishing this yummy recipe!
Vered DeLeeuw says
I'm so glad this recipe was a success, Lynn! It's interesting to learn that you can microwave it to melt the cheese. Thank you for this tip.
Patty says
I made this and it was a hit with my family. I’m going out of town and would like to bring this as a side dish. Can I make this, put it in a baking dish, refrigerate it and then bake it the next day? Thanks!
Vered DeLeeuw says
Yes, absolutely. If I were you, I would pre-cook the mushroom/onion mixture (steps 2,3) and put it in a food storage container. Bring the shredded cheese in a separate bag or container. When ready to bake the casserole, grease the baking dish, assemble the casserole (drain any liquids from the mushroom/onion mixture before adding it to the baking dish), and bake it.
Lija says
I'm a mushroom lover, so I can't wait to try this recipe. I liked your tip to broil rather than bake the casserole for 2-3 minutes until the cheese is melted. I was thinking I could actually use my air fryer that's like a toaster oven instead of lighting the big oven.
Also, since I always stir-fry mushrooms and onions when we have steak, I am looking forward to using this recipe when the husband grills steaks again. Thanks for the advice!
Vered DeLeeuw says
You're very welcome, Lija! I hope you enjoy it.