Homemade Green Bean and Mushroom Casserole

5 from 2 votes

Prep Time 45 mins

Cook Time 20 mins

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

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

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.

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.

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.

Preheat the oven to 350 degrees.
Spray a 9x13 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!