Thanksgiving day green bean casserole gets the star treatment with creamy mushrooms and gruyere topped with homemade fried leeks and onions. An easy side dish for holiday meals!
Here’s why we love this green bean casserole recipe so much:

- Traditional green beans versus haricot verts: They are interchangeable! The thing with French green beans (haricot verts) - they are thinner, and you don't need to blanch them. Traditional green beans are blanched beforehand to make them a bit more tender. However, you can use whichever you prefer!
- Umami: A salty cheese like gruyere is bursting with umami. Combined with the mushrooms and soy sauce and you've got yourself a huge Umami bomb!
- Olive Oil: High quality olive oil makes all the difference and adds such a beautiful buttery flavor, without the butter!
- Fried leeks + Onions: Traditional green bean casserole calls for a can of those pantry stable fried onions. With the simplest ingredients you can cook up your own fried onions! Leeks are a beautiful addition here because the texture is just a bit different than onions and they aren't quite as sweet. A nice yin and yang you might say.
- It’s quick! For a side dish that spends time in the oven, it really is quite quick to come together. In under 40 minutes you can have this side dish on your table.
How To Trim and Blanch Green Beans
Fresh green beans or haricot verts are typically sold trimmed and washed. If you are buying them fresh, cut the root end off of the bean. You can also snap the root end off as well.
To blanch green beans, bring a large pot of salted water to a boil. Once boiling, add green beans and cook for 4-5 minutes. We want them to be just cooked, not mushy. If you are using haricot verts, simply skip the blanching step!

This post is sponsored by O-Live & Co.. I was compensated for my time, however all opinions are always my own. Thank you for supporting the brands I use and love so much!
I’ve partnered up with my friends at O-Live & Co. to bring you a reinvented classic! Easy to prep and quick to cook the best type of holiday dishes!
O-Live & Co. is a sustainable company and the first carbon neutral olive oil brand. Their mill is located in the heart of their groves, allowing for their olives to be pressed within hours of picking, unlike other brands where olives are transported for days and become moldy. This gives the low acidity level of 0.2% compared to the average of 0.8% where olive are transported for days and become moldy. O-Live has won countless awards globally and scores 97/100 in the Flos Olei rankings, which is the world’s most prominent olive oil ranking system.
Today I am featuring their Organic Extra Virgin Olive Oil. This olive oil works fabulous with this green bean casserole because it is light in flavor. It works its magic by letting the other ingredients shine just as much as it does. It's the perfect oil for sautéing and fires up the leeks and onions beautifully.
Purchase stress-free directly through their online store or use their store locator to find where to purchase in-person near you today!
How To Cook Green Bean Casserole
Start by making your own mushroom soup.
- In a large pan begin by sautéing your onions. Add in your mushrooms until they become golden, then add your garlic.
- Then, stir in your flour and let it cook for about 1 minute before adding your broth.
- Add vegetable broth whisk it until it is incorporated with the flour.
- Stir in heavy cream and bring it to a simmer for 2-3 minutes.
- Whisk in gruyere, soy sauce, and season to taste with salt and pepper.
- Add your greens beans and toss everything together then add everything to a 9x13" baking dish and top with a bit more gruyere (duh!)

How To Make Fried Leeks and Onions
Our preferred method? Frying in olive oil.
- Thinly slice leeks and rinse well. Thinly slice onion and add to a bowl. Drain and dry off leeks a bit and add to the bowl with the onions.
- In a separate bowl, add flour.
- Heat olive oil in a large skillet over medium heat.
- Separate the leeks and onion slices and dredge in flour. Shake off the excess.
- In two batches, add onions and leeks to the hot pan and cook until golden brown, about 1-2 minutes, then flip and cook on the other side. Repeat with the remaining batches.
- Transfer to w towel lines plate to let them drain.
- Top green bean casserole with fried leeks and onions and bake for 20-25 minutes until the filling is bubbling.
That’s it! Green bean casserole could not be easier!
Recipe
Green Bean Casserole With Gruyere, Fried Leeks, and Onions
Ingredients
Green Bean Casserole
- 2 lbs. fresh green beans washed and trimmed
- 8 oz. mushrooms sliced
- 4 tablespoons Olive & Co. Organic Olive Oil
- 1 medium sweet/yellow onion diced
- 4 garlic cloves minced
- 4 tablespoons all purpose flour
- 1 ½ cups vegetable broth
- ¾ cup heavy cream
- 1 ½ cups gruyere cheese shredded and divided
- 1 teaspoon soy sauce
- Salt + pepper to taste
Fried Leeks and Onions
- 1 small sweet yellow onion thinly sliced
- 1 medium-large leek thinly sliced and washed well
- ½ cup all purpose flour
- 4 tablespoons Olive & Co. Organic Olive Oil
- Salt to taste
Instructions
- Make your fried leeks and onions; Thinly slices leeks and rinse well. Thinly slice your onion and add to a bowl. Drain and dry off the leeks a bit and add to bowl with onions. In a separate bowl add flour.
- In a large pan over medium heat, add olive oil.
- Separate the onion and leek slices and dredge in flour. Shake off the excess.
- In two batches, add onions and leeks to hot pan and cook until golden brown (about 1-2 minutes) then flip and cook on the other side.
- Transfer to a paper towel lined plate and let them drain.
- Make casserole; Preheat oven to 400 degrees F.
- Bring a large pot of salted water to a boil.
- Once boiling, add green beans to cook for 4-5 minutes, depending on their size. We want them to be just cooked, not mushy.
- Drain green beans and set aside.
- In a large pan over medium heat, add olive oil.
- Add diced onions and a sprinkle of salt and cook 3-4 minutes until softened.
- Add sliced mushrooms and a sprinkle of salt and cook for 3-4 minutes until just golden.
- Add garlic and cook for 30 seconds. Whisk in flour and cook for 1 minute.
- Pour in the vegetable broth and whisk until the flour is incorporated into the broth.
- Stir in the heavy cream and bring to a simmer to thicken for 2-3 minutes.
- Whisk in 1 cup of gruyere cheese, soy sauce, and season with salt and pepper to taste.
- Add the green beans and stir to combine.
- Add mixture to a 9x13 baking dish, sprinkle with the remaining ½ cup of gruyere cheese, and top with the fried onions and leeks.
- Bake for 20-25 minutes, or until the filling is bubbling.
- Let the casserole rest for 5 minutes before serving.
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