Green Bean Casserole

This is a twist on the classic green bean casserole. Made with baked onions and a mushroom cream sauce this side dish will be a hit for your Thanksgiving dinner, or any other time you want to eat this tasty dish. 

Green bean casserole was one of those dishes I used to shy away from when I was younger. The word casserole was synonymous with dry and bland to me, think elementary school cafeterias in the 90s. So it really took me a while to warm up to this dish. Then I had a friend tell me about how they made the dish and I wanted to try a version of it myself. This recipe is a far cry from what I thought about the first time I heard of this side dish. 

In this recipe

There are a lot of ingredients in this recipe but that is what makes it special.

Green beans: fresh green beans work best for this recipe however frozen is a great substitute. 

Roasted garlic: if you don’t have any just cut the top of a whole head of garlic wrap it in foil and bake at 375F for 45 minutes. You can always use regular garlic as well.

Baby portobello mushrooms: these have a meatier and richer flavor than other mushrooms but any sliced mushroom will do including shiitake and chanterelle. 

Nutmeg: A spice that will add a slight nutty flavor to the dish. 

Breadcrumbs: Will add a nice little crunch to the onions. I like to use panko. 

green bean casserole ingredients on a wooden cutting board
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Cooking the green beans

One of the important things about this dish to to cook the green beans before adding them to mushroom sauce. This does two things. The first is to reduce the cooking time, and the second is to season the green beans and also retain that lovely green color. First you want to heat the waiter to boiling and add enough salt that the water tastes like the ocean. Then cook for only 3-4 minutes before plunging them into the ice water. They will immediately stop cooking once they are added to the ice water and will finish cooking in the oven. This keeps them from getting mushy. 

Sliced onions covered in flour and breadcrumbs on a skeet pan
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skillet with cream and flour
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mushrooms cream sauce in a skillet
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Whisk that sauce

Once you have gotten the roux to a nice light caramel color you will want to switch to the whisk. This will help keep the milk and cream from scorching. Once it comes to a boil you will want to remove it from the heat. It won’t have completely thickened yet but that is ok because it will continue to thicken in the oven when it is baked. That is when you will stir the rest of the seasonings and the parmesan cheese. If you have thinly grated cheese it should melt into the sauce evenly and quickly. However it the cheese is of a thicker grate then you might have some chunks still in the sauce. 

Uncooked green bean casserole in a cast iron skillet
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cooked green bean casserole in a cast iron skillet
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Baking the green bean casserole

Once you add the mushrooms and then the green beans you will want to bake it for 15 minutes. This will give you a nice brown on the top as well as finish cooking the green beans. Also if you have some small chunks of parmesan then they will melt as well. Then you will add the onions on top and bake again for about 5 minutes to get an extra crisp from them. Now if you are like me and cannot get enough cheese top the whole thing off with a little bit more. 

A pan of green bean casserole on a cutting board
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Looking for other Thanksgiving sides?

Close up of green bean casserole in a cast iron skillet
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Green Bean Casserole

A special twist on the classic American side dish.
5 from 2 votes
Prep Time 10 minutes
Cook Time 50 minutes
Total Time 50 minutes
Course Side Dish
Cuisine American
Servings 8 servings
Calories 322 kcal


  • 12 inch cast iron skillet or casserole dish
  • Sheet pan
  • 2 Mixing Bowl
  • Large pot
  • Spider strainer or slotted spoon
  • Whisk


  • 2 pounds green beans ends cut

Mushroom sauce

  • 1 pound baby portobello mushrooms sliced
  • cup whole milk
  • ½ cup heavy cream
  • ½ cup parmesan cheese finely grated
  • ½ cup butter unsalted
  • 3 tablespoons flour
  • 2 tablepsoons roasted garlic about 4 - 5 cloves
  • ½ tablespoon thyme
  • 1 teaspoon salt
  • ½ tablespoon ground black pepper
  • ¼ teaspoon nutmeg

Onion topping

  • 1 onion thinly sliced
  • 3 tablespoons olive oil
  • 3 tablespoons flour
  • 2 tablespoons breadcrumbs
  • 1 tablespoon garlic powder
  • 1 teaspoon salt


  • Preheat the oven to 450°F, 230°C, or gas mark 8 and bring a large pot of salted water to a boil.

Making the onion topping

  • In a mixing bowl toss the onions in the olive oil. Then add the flour, salt, breadcrumbs, and garlic powder. Toss until the onions are evenly coated.
  • Place on a sheet pan and bake for 15 minutes tossing halfway. Remove from the oven.
  • Once they are done reduce the heat to 375°F, 190°C, or gas mark 5.

Cooking the green beans

  • Fill a large mixing bowl with ice water and set next to the stove.
  • Once the water has started boiling add half of the green beans and cook for 3-4 minutes. Strain from the water and immediately plunge into the ice water. Repeat with the remaining green beans. Pour out the water once all of the beans are chilled.

Making the mushroom cream sauce

  • In a cast iron skillet on medium-high, heat 4 tablespoons of the butter. Once it has melted add the mushrooms, salt, pepper, and thyme. Leave to cook undisturbed for 2 minutes before stirring and flipping over. Allow the other side to cook undisturbed for another 2 minutes. Add the roasted garlic, stir and continue to cook until done. Remove from the pan and place into a bowl.
  • Return the pan to the heat and melt the remaining 4 tablespoons of butter. Add the flour and stir until the flour starts to darken to a light caramel color. About 3-5 minutes. Add the milk and cream and whisk until combined. Keep whisking and bring to a boil. remove from the heat and add nutmeg and parmesan cheese.
  • Stir in the mushrooms and green beans. Bake for 15 minutes. Add the onion topping and bake for another 5 minutes.


Serving: 1servingCalories: 322kcalCarbohydrates: 19gProtein: 7gFat: 25gSaturated Fat: 13gPolyunsaturated Fat: 2gMonounsaturated Fat: 9gTrans Fat: 0.5gCholesterol: 56mgSodium: 458mgPotassium: 372mgFiber: 4gSugar: 7gVitamin A: 1489IUVitamin C: 16mgCalcium: 190mgIron: 2mg
Nutrition Disclaimer*
Keyword Green Beans, Holiday, Mushroom, Thanksgiving
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green bean casserole pinterest pin
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