Maybe because I’m Southern, or maybe just because they’re good, but I do love a hearty casserole. It’s vegetables, maybe a starch, maybe a protein. Deliciously creamy sauce, some kind of crunchy topping…there’s just so many possibilities! One of the best versions is a completely homemade green bean and mushroom casserole. I think because I wait until the end of the year to make it, and we only make it a few times, it holds a special place for me.
Conjuring up holiday tables brimming with food, loud chatter mingling in the air with wafts of special dishes, and family bumping elbows and balancing plates on laps are precious memories inextricably tied with food.
Because of those memories, I’ll never denounce a canned version of this casserole. I love it that way too because people I love made it that way, so this is not a condemnation. It’s a preference. I love all the work that goes into these components, and I hope it shows in every bite.
Homemade Fried Onions for the Topping
I’ve had plenty of holidays with this casserole topped with those fried shallots we only see around this time of year, and they work perfectly well. If you prefer them, use them! If you want to make your own, you have a couple of options.
- Bake them. You can get crispy onions from the oven, baked on parchment paper.
- Deep fry them. Going the traditional route will give you some delicious onions, for sure, but of course is higher in fat.
- Air fry them. This is a pretty great route if you have and love this appliance.
I’m going traditional with this recipe and frying the onions. This is a great beginner recipe for deep frying if, like me, frying scares the living finger burns out of you. Truly, though, like just about all my recipes, do what works best for you here! There are a bunch of ways to make the onions, so do what you and your family loves best!
Making the Sauce for Homemade Green Bean & Mushroom Casserole from Scratch
If we are making fried onions, we are definitely making the sauce! This is truly what elevates this dish out of the ’60s and straight into the now.
To make this sauce, you will build it straight into the same skillet where you cook the mushrooms and onions. After cooking the vegetables, you sprinkle the flour on, stirring to combine. Then, you cook the mixture for a minute or two before adding the liquid to make a cohesive sauce.
This is a typical kind of white sauce that is perfect for casseroles like this where you want creaminess but you don’t necessarily want cheesiness. We’ll add cheese to the top, but it doesn’t need to be throughout.
This creamy mushroom sauce is delicious, but if you have a mushroom hater in your midst, you can omit them or replace them with bell pepper or peas. Like all my recipes, make it yours!
So Many Ways to Make this Ahead!
If you are making this dish for a holiday, I know you’re concerned about oven space and time. Luckily, you can prep this dish ahead of time, and it only takes about 15 more minutes in the oven to be finished. This holiday staple can be made ahead in various ways with various resulting times. Let’s walk through it piece by piece.
The Onions: you can make your onions, no matter which method you use, up to 1 month ahead of time. Store them in an airtight container in the fridge. They will “wake up” again in the oven when you bake the casserole.
The Sauce: Arguably the hardest part, the sauce can be made and stored in an airtight container in the fridge up to 4 days ahead.
The Beans: The beans can be blanched and stored, unsalted, in an airtight container in the fridge for 3-5 days ahead.
The Whole Shebang: You can totally make the entire casserole, keeping the onions separate, up to 3 days ahead of time. When you’re ready to cook it, just top it with the onions and bake.
With that many options, anyone has time to make this comforting holiday staple from scratch!
Tips for Prepping Homemade Green Bean & Mushroom Casserole
This recipe makes a 9×13 casserole dish worth of comfy goodness. You can definitely half the recipe pretty easily to make a portion better suited to a weekday meal or smaller family.
You can store leftovers for up to 3 days covered tightly with foil or in an airtight container.
Substitute shallots for onions, add some chopped pecans to the topping, leave out the mushrooms, add fresh thyme or dill…there are so many ways to make this your own. Experiment and find the perfect tweaks to make this your family’s favorite!
Homemade Green Bean and Mushroom Casserole
- 9×13 casserole dish
- Large mixing bowl
- Large pot
- Baking sheet and parchment paper
For the Green Beans
- 2 pounds fresh green beans
- 4-5 cups water
- 1 teaspoon salt
For the Creamy Mushroom Sauce
- 3 cups white button mushrooms, sliced
- 1/2 cup diced onion
- 3 tablespoons AP flour Optional: I tested this with Bob's Red Mill 1-to-1 Gluten Free Baking Flour, and it was awesome. Subbing the flour here would make this recipe gluten free.
- 3 tablespoons unsalted butter
- 1.5 cups half and half
- 1.5 cups vegetable stock or bone broth
- 3 cloves garlic, minced
- 1 teaspoon dried thyme
- 1/4 teaspoon freshly grated nutmeg
For the Fried Onions
- 3 cups thinly sliced, half-moon shaped onions
- 3 cups vegetable oil
- 2 eggs
- 1.5 cups AP flour Optional: I tested this with Bob's Red Mill 1-to-1 Gluten Free Baking Flour, and it was awesome. Subbing the flour here would make this recipe gluten free.
- 1 teaspoon salt
- 1/2 teaspoon ground black pepper
To Make the Fried Onions
- Add the vegetable oil to a heavy bottomed, wide pan (like a Dutch oven) over medium high heat.
- Peel and cut your onion in half, stem to top. Thinly slice your onion into half moon shapes.
- Prep a draining station by placing a wire cooling rack over a baking sheet. For the easiest cleanup, line the baking sheet with aluminum foil first.
- In a medium bowl, beat the two eggs until completely mixed.
- In another bowl, add the flour, salt, and pepper.
- Working in batches by the handful, dip the onions first in the egg and completely coat them. Then, dip that same batch into the flour mixture, tossing completely to coat.
- Fry the coated onions until golden brown, flipping carefully as needed to get even browning.
- Remove them from the pot. Set them on the draining station and immediately sprinkle with salt. Repeat this process until all your onions are cooked.
- If using right away, let them wait on the draining station until you are ready to use them. If making ahead, let them cool to room temperature, then store in an airtight container in the fridge.
To Make the Green Beans
- Add 4-5 cups of water to a large pot. Add the salt. Bring water to a boil.
- While the water is coming to a boil, trim the ends off your green beans. Cut them into 1.5" long pieces, or pieces the size you want in your casserole. Wash and pat dry.
- Once the water is boiling, add the green beans. Cook for about 4-5 minutes.
- While they are cooking, prepare an ice water bath in a bowl.
- After 4-5 minutes, when beans are fork tender and bright green, drain them from the hot water. Add them immediately to the ice water bath.
- Let them chill there for 5 minutes.
- Set them aside if using now. If you are making them ahead, pat them dry and store them in an airtight container in the fridge.
To Make the Creamy Mushroom Sauce
- Make sure your ingredients are ready to go before beginning. Wash, pat dry, and slice your mushrooms. Dice the onion. Mince the garlic. If you are using any fresh herbs, make sure they are washed and minced.
- Add the butter to a heavy skillet over medium heat. Let it melt but not bubble.
- Add the onion, sprinkle with a pinch of salt, and saute for about 5 minutes.
- Add the mushrooms, sprinkle with a pinch of salt, and saute for at least 5-7 minutes. We want them to release some of their liquid, so expect them to steam and shrink. Stir as needed.
- Add the garlic and all spices. Saute for 1 minute.
- Stir in the vegetable stock or bone broth and simmer for 1-2 minutes.
- Decrease the heat to medium-low. Add the half and half, gently stirring to combine.
- Cook until the mixture thickens, about 7-9 minutes.
- Taste and adjust the salt and pepper levels if needed.
- Remove from heat. If using now, continue to the next step. If making ahead, let it cool to room temperature, then store in an airtight container in the fridge.
To Make the Entire Casserole
- Preheat the oven to 350 degrees.
- Spray a 9×13 casserole dish with nonstick spray. You could alternatively grease the inside with softened butter.
- In a large bowl, stir together the green beans and creamy mushroom sauce.
- Add the mixture to the casserole dish, spreading into an even layer.
- Top with the onions.
- Bake at 350 degrees for 15-20 minutes. Remove and serve hot!